Dissertations / Theses on the topic 'Wave turbulence interaction'
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1
Teixeira, Miguel Angelo Cortez. "Interaction of turbulence with a free surface." Thesis, University of Reading, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340045.
2
Wheadon, Andrew John. "Wave-turbulence interaction in shallow water numerical models : asymptotic limits, and subgrid interactions." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34333.
Abstract:
The ability to directly simulate all atmospheric motion is currently well beyond the limits of the computers available to us. As such techniques must be developed that accurately model important processes in an affordable manner. Large-scale balanced motion is well understood, but as affordable resolution increases, models are able to resolve scales where large-scale turbulence and small-scale waves are important. This requires a new set of techniques that respect the interactions between these different kinds of motion. In this thesis we look at two ways of assessing the accuracy of models capable of representing the scales at which these interactions occur. The first approach uses asymptotic limit solutions to derive a set of terms whose scale is known. These terms can then be evaluated as the model approaches a relevant asymptotic regime, and a `good' model should reproduce the expected rate of scaling. We apply this method of asymptotic limit solutions to an Eulerian and a Lagrangian shallow water model. The former is based upon ENDGame, the model currently in use at the Met Office, and the latter is based upon a candidate model from GungHo which is seeking a replacement for ENDGame. In addition, the Eulerian model is evaluated with both small and large timesteps and the results confirm the ability of the semi-implicit scheme to retain accuracy at large timesteps. Errors in the higher-order diagnostics used in this section highlight the need to make these analytic diagnostics consistent with the discretisations of the model in question. The second method involves looking at the exchanges of energy in a spectral shallow water model in order to inform the design of subgrid models. By running a high-resolution simulation and truncating the energy at a certain wavenumber, comparing the result to a run without truncation shows the contribution of the scales below the truncation limit. We extend this by separating the total energy into separate components that may be truncated and evaluated individually in order to give a more complete picture of energy exchanges at the subgrid scale.
3
Dong, P. "The computation of wave-induced circulations with wave current interaction and refined turbulence modelling." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47036.
4
Jennings, Ross. "Empirical modelling of turbulence and wave-current interaction in tidal streams." Thesis, University of Hull, 2017. http://hydra.hull.ac.uk/resources/hull:16600.
Abstract:
The successful development of the tidal stream power industry fundamentally relies on a thorough, quantitative understanding of the available resource. Numerical simulations and laboratory flume experiments have demonstrated that increased turbulence and wave-induced motion can have detrimental effects on the fatigue and performance of prototype tidal stream turbines (TSTs). Knowledge of the relationships between mean current velocity, turbulence and surface waves is limited and presents a significant research gap. This research makes a significant contribution to the field by developing empirical models from in situ data collected within the Humber Estuary. These models estimate the turbulence strength and intensity at a point and through depth given a mean current velocity. An 18-day deployment of bed-mounted directional wave recorders (DWR) at Foul Holme Spit simultaneously recorded two-dimensional flow velocities and surface wave parameters. Static, vessel-mounted, acoustic Doppler current profiler (ADCP) surveys recorded turbulence through depth near St. Andrews Dock. The analyses revealed distinct relationships between the mean current velocity, turbulence strength and turbulence intensity at a point which are comparable to recently published results. The inter-tidal relationship between streamwise mean current velocity and turbulence strength is modelled at a point using power regression where α is 0.13 and β is 0.72 with an R2 value of 0.8721. The inter-tidal relationship between streamwise mean current velocity and turbulence intensity is modelled at a point using power regression where γ is 14.315 and δ is -0.2316 with an R2 value of 0.5482. A newly defined empirical relationship between depth-averaged mean current velocity and turbulence intensity is modelled using power regression where ε is 17.75 and ζ is -0.94 with an R2 value of 0.7912. The models derived at a point are tested on the data collected through depth and exhibited strong predictive capability within the order of 0.1 ms-1. The exponential approximation of wave-induced velocity, proposed by Soulsby (2006), was tested and shown to be inappropriate for estimating wave-induced velocities at this scale. A comparative spectral analysis between DWR sample bursts determined that spikes in the turbulence spectra can be attributed to surface wave parameters, thus validating the conceptual model proposed by Soulsby and Humphrey (1990).
5
Wenger, Christian W. "Analysis of Two-point Turbulence Measurements for Aeroacoustics." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/30837.
Abstract:
Simultaneous two-point three-component four-sensor hot-wire velocity measurements taken in three flows of aeroacoustic interest are here analyzed. The analyses provide information on the turbulence structure of the flows as it would be encountered by hypothetical noise producing blades passing through the flows. Two-point measurements taken in the first flow, a lifting wake from a rectangular NACA 0012 half wing, are used to calculate space-time correlation functions and 'pointwise' wave number frequency spectra. Two upwash spectra, calculated for locations in the region of the wake that is roughly homogenous in the spanwise direction, are direct estimates of the full wave number frequency spectra at their locations. As such, they are used to perform aeroacoustic calculations, and the results are compared to results achieved using the von Kármán isotropic spectrum. Amiet's approximation, where the wave number frequency spectra can be represented by the correlation length scales is found to hold reasonably well for the measured spectra.
The two-point measurements in the second flow, a vortex/blade-tip interaction, are analyzed to provide information useful to researchers of blade-wake interaction noise produced by helicopter rotors. Space-time correlation functions and wave number frequency spectra are calculated for five cuts through the region of interaction. The correlation functions provide information concerning the turbulence length scales found in the interaction region. The spectra are compared to the von Kármán isotropic spectrum and found to be greatly different. However, the spectra do bear some resemblance to spectra calculated in the spanwise homogenous region of the lifting wake.
The two-point measurements taken in the third flow, the wake from a fan cascade, are analyzed to provide information of use to modelers of broadband noise produced through rotor wake/stator interactions. In particular, space-time correlation functions are calculated for a grid of two-point measurements, which allows the estimation of the turbulence structure as seen by a passing stator blade. Space-time correlation functions and wave number frequency spectra are calculated for various stator configurations. The implications of engine operating speed and stator configuration for broadband noise production are discussed.
[Vita removed March 2, 2012. GMc]
Master of Science
6
Mohamed, Ahmed. "Nonlinear inertial waves focusing in rotating flows." Electronic Thesis or Diss., Ecully, Ecole centrale de Lyon, 2023. http://www.theses.fr/2023ECDL0058.
Abstract:
Nous étudions la propagation des ondes inertielles générées par l’oscillation d’un tore axisymétrique dans un fluide en rotation. Ces ondes inertielles se propagent à partir du tore oscillant avec un angle de propagation θf, déterminé par la relation de dispersion. Elles convergent vers une région focale où des interactions non linéaires peuvent induire une turbulence. Notre étude utilise des simulations numériques directes pour modéliser cet écoulement, en tenant compte des régimes linéaires et non linéaires, et en utilisant deux configurations de forçage du tore. Le premier modèle simplifie le tore en tant que force volumique locale en utilisant une fonction delta de Dirac (anneau de Dirac) le long de la direction d’oscillation du tore dans les équations de conservation de la quantité de mouvement. Le deuxième modèle, plus réaliste, met en œuvre un tore en 3D en utilisant la méthode de pénalisation. Nos résultats révèlent l’émergence d’un vortex central résultant des interactions non linéaires des ondes inertielles propagées. Dans le cas de l’anneau de Dirac et du régime linéaire, nos résultats montrent une relation entre l’énergie cinétique verticale et l’angle de propagation au point focal, avec une énergie maximale se produisant à θf = 35o. De même, dans le scénario de forçage en 3D du tore, aussi bien dans les simulations linéaires que non linéaires, indiquent un angle optimal de θf = 30o, conduisant à une vitesse verticale maximale et à une dissipation maximale, signifiant un transfert efficace d’énergie de la source oscillante vers la région focale. Dans le régime non linéaire, nous présentons la distribution spectrale détaillée de l’énergie cinétique dans la zone focale et effectuons une analyse spatio-temporelle du champ de vitesse. Cette analyse identifie les résonances triadiques des ondes inertielles, qui génèrent une zone turbulente et un mode à grande échelle similaire à l’écoulement moyen géostrophiqueWe investigate the propagation of inertial waves generated by the oscillation of an axisymmetric torus in a rotating fluid. These inertial waves propagate from the oscillating torus with a propagation angle θf, determined by the dispersion relation. They focus to a focal region where nonlinear interactions may induce turbulence. Our study employs direct numerical simulations to model this flow, considering both linear and nonlinear regimes, and using two torus forcing configurations. The first model simplifies the torus as a local volume force using a Dirac delta function (Dirac ring) along the torus’s oscillation direction in the momentum conservation equations. The second, more realistic model implements a 3D torus using the penalization method. Our findings reveal the emergence of a central vortex as a result of the nonlinear interactions of the propagated inertial waves. In the case of the Dirac ring and the linear regime, our results demonstrate a relationship between vertical kinetic energy and propagation angle at thefocal point, with maximum energy occurring at θf = 35o. Similarly, in the 3D torus forcing scenario, both linear and nonlinear simulations indicate an optimal angle of θf = 30o, leading to maximum vertical velocity and dissipation, signifying efficient energy transfer from the oscillating source to the focal region. In the nonlinear regime, we show the detailed spectral distribution of kinetic energy within the focal zone and conduct spatio-temporal analysis of the velocity field. This analysis identifies triadic resonances of the inertial waves, which drive the generation of a turbulent patch and a large-scale mode similar to the geostrophic mean flow
7
Gallagher, Stephen J. "Zonal flow generation through four wave interaction in reduced models of fusion plasma turbulence." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/59703/.
Abstract:
In tokamaks, turbulence is a key contributor to cross field transport. However, it is also responsible for the spontaneous generation of large scale structures such as zonal ows. These are of relevance to fusion plasmas as they can create transport barriers which aid plasma confinement. The interaction between drift waves and zonal ows can be investigated using reduced models such as the Hasegawa- Mima and Hasegawa-Wakatani equations. A four-wave truncated model is developed for the Extended-Hasegawa-Mima (EHM) equation. This produces a set of four ordinary differential equations (ODEs) that are used to investigate the modulational instability (MI), a mechanism by which drift waves can produce a zonal ow. These equations are linearised to produce a dispersion relation for the MI which is used to produce a set of maps of the linear growth rate of the MI. These show how additional modes become unstable as the gyroradius is increased. The truncated model and dispersion relation are then compared to measurements taken from simulations of the full EHM partial differential equation (PDE) which has been seeded with an appropriate initial condition. Good agreement is found when the pump wave has no component in the direction of the density gradient. A similar truncated model is derived for the Extended-Hasegawa-Wakatani (EHW) equations. As the EHW system has separate equations for density and potential this leads to a set of eight ODEs. The linearisation technique used for the EHM system cannot be applied here. Instead, approximations based on the built in EHW instability are made to calculate a linear growth rate for the zonal ow using the ODEs describing it. These analytical predictions are then compared to a full PDE simulation of the system, which is initialised using random noise. It is found that for particular sets of waves the ODEs provide a good prediction of the linear growth rate. A driving term is added to the EHM equation to reproduce the effect of the built in instability of the EHW equations. This causes a drift wave spectrum to grow when full EHW PDE simulations are seeded with random noise. The four-wave ODE model is updated to include this driving. The ODE model again produces good predictions for the growth rate of the zonal flow.
8
Hornung, Grégoire. "Etude de la turbulence plasma par réflectrométrie à balayage ultra-rapide dans le tokamak Tore Supra." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4741/document.
Abstract:
La turbulence plasma engendre un transport anormal de la chaleur et des particules qui dégrade l’efficacité d’un réacteur de fusion. La mesure de la turbulence plasma dans un tokamak est donc essentielle à la compréhension et au contrôle de ce phénomène. Parmi les instruments de mesure à disposition, le réflectomètre à balayage installé sur le tokamak Tore Supra a accès à la densité du plasma et ses fluctuations depuis le bord jusqu’au centre des décharges, avec une excellente résolution spatiale (mm) et temporelle (µs), de l’ordre des échelles de la turbulence. Cette thèse est dédiée à la caractérisation de la turbulence plasma dans Tore Supra à partir de mesures de réflectométrie à balayage ultrarapide. Des analyses de corrélations ont permis d’évaluer les échelles spatiales et temporelles de la turbulence ainsi que sa vitesse radiale. Dans la première partie, la caractérisation des propriétés de la turbulence à partir des profils de densité reconstruits est discutée, notamment au travers d’une comparaison avec les données des sondes de Langmuir. Ensuite une étude paramétrique est présentée mettant en relief l’effet de la collisionalité sur la turbulence, dont une interprétation est proposée en termes de stabilisation d’une turbulence électronique due aux électrons piégés. Finalement, on illustre comment le chauffage additionnel produit une modification locale de la turbulence dans le plasma proche des parois, se traduisant par une augmentation de la vitesse des structures et une diminution de leur temps de corrélation. L’effet supposé des potentiels rectifiés générés par l’antenne est étudié à l’aide de simulationsThe performance of a fusion reactor is closely related to the turbulence present in the plasma. The latter is responsible for anomalous transport of heat and particles that degrades the confinement. The measure and characterization of turbulence in tokamak plasma is therefore essential to the understanding and control of this phenomenon. Among the available diagnostics, the sweeping reflectometer installed on Tore Supra allows to access the plasma density fluctuations from the edge to the centre of the plasma discharge with a fine spatial (mm) and temporal resolution (µs ) , that is of the order of the characteristic turbulence scales.This thesis consisted in the characterization of plasma turbulence in Tore Supra by ultrafast sweeping reflectometry measurements. Correlation analyses are used to quantify the spatial and temporal scales of turbulence as well as their radial velocity. In the first part, the characterization of turbulence properties from the reconstructed plasma density profiles is discussed, in particular through a comparative study with Langmuir probe data. Then, a parametric study is presented, highlighting the effect of collisionality on turbulence, an interpretation of which is proposed in terms of the stabilization of trapped electron turbulence in the confined plasma. Finally, it is shown how additional heating at ion cyclotron frequency produces a significant though local modification of the turbulence in the plasma near the walls, resulting in a strong increase of the structure velocity and a decrease of the correlation time. The supposed effect of rectified potentials generated by the antenna is investigated via numerical simulations
9
Asproulias, Ioannis. "RANS modelling for compressible turbulent flows involving shock wave boundary layer interactions." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/rans-modelling-for-compressible-turbulent-flows-involving-shock-wave-boundary-layer-interactions(e2293c9d-de93-4e97-b8b8-967ec0b682d8).html.
Abstract:
The main objective of the thesis is to provide a detailed assessment of the performance of four types of Low Reynolds Number (LRN) Eddy Viscosity Models (EVM), widely used for industrial purposes, on flows featuring SWBLI, using experimental and direct numerical simulation data. Within this framework the two-equation linear k-ε of Launder and Sharma (1974) (LS), the two-equation linear k-ω SST, the four-equation linear φ-f of Laurence et al. (2004) (PHIF) and the non-linear k-ε scheme of Craft et al. (1996b,1999) (CLSa,b) have been selected for testing. As initial test cases supersonic 2D compression ramps and impinging shocks of different angles and Reynolds numbers of the incoming boundary layer have been selected. Additional test cases are then considered, including normal shock/isotropic turbulence interaction and an axisymmetric transonic bump, in order to examine the predictions of the selected models on a range of Mach numbers and shock structures. For the purposes of this study the PHIF and CLSa,b models have been implemented in the open source CFD package OpenFOAM. Some results from validation studies of these models are presented, and some explorations are reported of certain modelled source terms in the ε-equation of the PHIF and CLSb models in compressible flows. Finally, before considering the main applications of the study, an examination is made of the performance of different solvers and numerical methods available in OpenFOAM for handling compressible flows with shocks. The performance of the above models, is analysed with comparisons of wall-quantities (skin-friction and wall-pressure), velocity profiles and profiles of turbulent quantities (turbulent kinetic energy and Reynolds stresses) in locations throughout the SWBLI zones. All the selected models demonstrate a broadly consistent performance over the considered flow configurations, with the CLSb scheme generally giving some improvements in predictions over the other models. The role of Reynolds stress anisotropy in giving a better representation of the evolution of the boundary layer in these flows is discussed through the performance of the CLSb model. It is concluded that some of the main deficiencies of the selected models is the overestimation of the dissipation rate levels in the non-equilibrium regions of the flow and the underestimation of the amplification of Reynolds stress anisotropy, especially within the recirculation bubble of the flows. Additionally, the analysis of the performance of the considered EVM's in a normal shock/isotropic turbulence interaction illustrates some drawbacks of the EVM formulation similar to the ones observed in normally-strained incompressible flows. Finally, a hybrid Detached Eddy Simulation (DES) approach is incorporated for the prediction of the transonic buffet around a wing.
10
Stamatiou, Evangelos. "Experimental investigation of the wave-turbulence interaction at low reynolds numbers in a horizontal open-channel flow." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0007/MQ40914.pdf.
11
PERUZZI, COSIMO. "Turbulence Properties of Smooth-Bed Open-Channel Flows with and without Collinear Gravity Waves." Doctoral thesis, Politecnico di Torino, 2020. http://hdl.handle.net/11583/2845794.
12
Couldrick, Jonathan Stuart Aerospace Civil & Mechanical Engineering Australian Defence Force Academy UNSW. "A study of swept and unswept normal shock wave/turbulent boundary layer interaction and control by piezoelectric flap actuation." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Aerospace, Civil and Mechanical Engineering, 2006. http://handle.unsw.edu.au/1959.4/38672.
Abstract:
The interaction of a shock wave with a boundary layer is a classic viscous/inviscid interaction problem that occurs over a wide range of high speed aerodynamic flows. For example, on transonic wings, in supersonic air intakes, in propelling nozzles at offdesign conditions and on deflected controls at supersonic/transonic speeds, to name a few. The transonic interaction takes place at Mach numbers typically between 1.1 and 1.5. On an aerofoil, its existence can cause problems that range from a mild increase in section drag to flow separation and buffeting. In the absence of separation the drag increase is predominantly due to wave drag, caused by a rise in entropy through the interaction. The control of the turbulent interaction as applied to a transonic aerofoil is addressed in this thesis. However, the work can equally be applied to the control of interaction for numerous other occurrences where a shock meets a turbulent boundary layer. It is assumed that, for both swept normal shock and unswept normal shock interactions, as long as the Mach number normal to the shock is the same, then the interaction, and therefore its control, should be the same. Numerous schemes have been suggested to control such interaction. However, they have generally been marred by the drag reduction obtained being negated by the additional drag due to the power requirements, for example the pumping power in the case of mass transfer and the drag of the devices in the case of vortex generators. A system of piezoelectrically controlled flaps is presented for the control of the interaction. The flaps would aeroelastically deflect due to the pressure difference created by the pressure rise across the shock and by piezoelectrically induced strains. The amount of deflection, and hence the mass flow through the plenum chamber, would control the interaction. It is proposed that the flaps will delay separation of the boundary layer whilst reducing wave drag and overcome the disadvantages of previous control methods. Active control can be utilised to optimise the effects of the boundary layer shock wave interaction as it would allow the ability to control the position of the control region around the original shock position, mass transfer rate and distribution. A number of design options were considered for the integration of the piezoelectric ceramic into the flap structure. These included the use of unimorphs, bimorphs and polymorphs, with the latter capable of being directly employed as the flap. Unimorphs, with an aluminium substrate, produce less deflection than bimorphs and multimorphs. However, they can withstand and overcome the pressure loads associated with SBLI control. For the current experiments, it was found that near optimal control of the swept and unswept shock wave boundary layer interactions was attained with flap deflections between 1mm and 3mm. However, to obtain the deflection required for optimal performance in a full scale situation, a more powerful piezoelectric actuator material is required than currently available. A theoretical model is developed to predict the effect of unimorph flap deflection on the displacement thickness growth angles, the leading shock angle and the triple point height. It is shown that optimal deflection for SBLI control is a trade-off between reducing the total pressure losses, which is implied with increasing the triple point height, and minimising the frictional losses.
13
Diop, Moussa. "Transition à la turbulence en écoulements compressibles décollés." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0473/document.
Abstract:
Les recherches sur les instationnarités des Interactions Ondes de Choc Couches Limites (IOCCL) turbulentes ont permis une description détaillée de celles-ci tant expérimentalement que numériquement . Ceci a conduit à plusieurs schémas susceptibles d'expliquer les respirations à basses fréquences observées dans de tels écoulements. Les configurations avec des conditions amont laminaires ou transitionnelles ont été moins étudiées.Dans le cadre du programme Européen TFAST, un important effort a été mené afin de développer des dispositifs expérimentaux, conjointement à des simulations numériques, permettant une étude détaillée de ces configurations. Dans le cadre de cette thèse, on a mis en place une configuration de réflexion d'onde de choc sur une couche limite laminaire pour un nombre de Mach de 1.68. L'utilisation des métrologies classiques (Anémométrie Laser Doppler, Anémométrie Fil Chaud), adaptées à ces conditions expérimentales particulières, a permis de décrire les propriétés spatio-temporelles de ces écoulements. Le champ moyen a été caractérisé et comparé aux théories classique et aux résultats obtenus dans différentes souffleries.Un schéma décrivant le mécanisme de transition à la turbulence au sein de l'interaction a été développé. Sa sensibilité aux conditions amont a été étudiée en plaçant des perturbations en amont de l'interaction. Dans tous les cas, des instationnarités convectives (haute fréquence) et stationnaires (basse fréquence) ont été observées et comparées à celles existantes pour les configurations amont turbulentes. Une gamme intermédiaire d'instationnarités convectives (moyenne fréquence) a été mise en évidence et caractériséeResearch dedicated to the study of the unsteadiness of turbulent Shock Wave Boundary Layer Interaction (SWBLI) has allowed a detailed description of this kind of interaction both experimentally and numerically. Several scenario were proposed to explain the low frequency unsteadiness observed in separated SWBLI. Nevertheless, the literature on this kind of flow involving either upstream laminar or transitional conditions is quite reduce. Within the framework of the European TFAST program, an important effort was made to develop experimental devices, in conjunction with numerical simulations, allowing a detailed study of these laminar or transitional configurations. In particular, within the framework of this thesis, a shock wave reflection configuration on a laminar boundary layer was set-up, with a nominal free stream Mach number of 1.68. Using classical metrology (Laser Doppler Anemometry, Hot WireAnemometry) that have been adapted to these particular experimental conditions, we have been able to describe the spatio-temporal properties of the interaction. The mean field has been characterized and compared with the classical theories and the results obtained in other configurations.A model describing the transition mechanisms to turbulence within the interaction has been developed. Its sensitivity to upstream conditions was studied by placing perturbations upstream of the interaction. In all cases, convective (high frequency) and stationary (low frequency) unsteadiness were observed and compared with those existing for upstream turbulent configurations. An intermediate range of convective unsteadiness (medium frequency) has been demonstrated and characterized
14
Crespo, Matthieu. "Etude de l'interaction entre une onde de choc et une turbulence cisaillée en présence de gradients moyens de température et de masse volumique." Thesis, Toulouse, INPT, 2009. http://www.theses.fr/2009INPT039H/document.
Abstract:
Cette étude a été l'occasion d'étudier les effets liés à la présence d'un cisaillement particulier de l'écoulement moyen sur le phénomène d'interaction choc/turbulence. Dans un premier temps, un outil de calcul performant et modulaire fondé sur une approche orientée objet a été développé afin de réaliser des simulations numériques directes de ce type d'écoulement. L'utilisation de schémas numériques à capture de choc et d'ordre élevé de type WENO ont permis une résolution fidèle des équations de Navier-Stokes compressibles. Dans un deuxième temps, une analyse poussée des effets de ce type de cisaillement sur la turbulence en l'absence de choc a été réalisée. Cette première étude a été l'occasion de dégager l'influence de plusieurs paramètres influents pour cette configuration d'écoulement. Enfin, dans un dernier temps, l'étude du phénomène d'interaction choc/turbulence cisaillée en présence de gradients moyens de température et de masse volumique a permis de souligner l'activation de phénomènes physiques caractéristiques à cette configuration. Ce travail permet également d'apporter une base de données de résultats susceptible d'être confrontée avec les modèles de turbulence et constitue un point de vue intéressant pour l'étude du phénomène d'interaction choc/couche limiteThis study sheds some light on the effects of a specific sheared flow over the shock / turbulence interaction phenomenon. An efficient and modular computational tool using an oriented object approach has first been developed in order to carry out direct numerical simulations of this configuration. The use of high order shock capturing schemes allows to solve accurately the turbulent flow, even in presence of physical discontinuities. A detailed study concerning the effects of this specific mean shear on the turbulent flow has then been conducted in a shock-free configuration. This preliminary study emphases some significant parameters of this flow configuration. In a second step, DNS of the interaction between the turbulent shear flow and a normal shock ware are performed. These simulations are compared to the isotropic turbulence / shock interaction situation, which allows to underline the activationof specific mechanisms due to the presence of the mean shear in the upstream flow. An interesting database is now available and can be used to assess and improve turbulence models. This is also an interesting point of view for studying the shock/boundary layer interaction phenomenon
15
Rendu, Quentin. "Modélisation des écoulements transsoniques décollés pour l'étude des interactions fluide-structure." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1328/document.
Abstract:
Les écoulements transsoniques rencontrés dans le cadre de la propulsion aéronautique et spatiale sont associés à l'apparition d'ondes de choc. En impactant la couche limite se développant sur une paroi, un gradient de pression adverse est généré qui conduit à l'épaississement ou au décollement de la couche limite. Lors de la vibration de la structure, l'onde de choc oscille et interagit avec la couche limite, générant une fluctuation de la pression statique à la paroi. Il s'ensuit alors un échange d'énergie entre le fluide et la structure qui peut être stabilisant ou au contraire conduire à une instabilité aéroélastique (flottement). La modélisation de la réponse instationnaire de l'interaction onde de choc / couche limite pour l'étude des interactions fluide-structure est l'objet de ce travail de recherche. Il s'appuie sur la résolution des équations de Navier-Stokes moyennées (RANS) et la modélisation de la turbulence. Les méthodes et modèles utilisés ont été validés à partir de résultats expérimentaux issus d'une tuyère transsonique dédiée à l'étude des interactions fluide-structure. Ces travaux sont ensuite appliqués à l'amélioration de la prédiction du flottement en turbomachine. Une méthode linéarisée en temps permettant la résolution des équations RANS dans le domaine fréquentiel est utilisée. Nous confirmons l'importance de la dérivation du modèle de turbulence lors de la prédiction d'une interaction forte entre une onde de choc et une couche limite décollée. Une méthode de régularisation est présentée puis appliquée aux opérateurs non dérivables du modèle de turbulence k-! de Wilcox (2006). La prédiction de la réponse instationnaire de l'interaction onde de choc / couche limite dans une tuyère est évaluée à partir de simulations bidimensionnelles et présente un bon accord avec les données expérimentales. En évaluant l'influence de la fréquence réduite, une instabilité aéroélastique de type flottement transsonique est identifiée. Un dispositif de contrôle, reposant sur la génération d'ondes de pression rétrogrades à l'aval de la tuyère, est proposé puis validé numériquement. Enfin, une méthodologie est proposée pour comprendre les mécanismes aérodynamiques conduisant au flottement. Pour cela, il a été réalisé un dessin provisoire d'une soufflante transsonique à fort taux de dilution. Cette soufflante, l'ECL5, est destinée à l'étude expérimentale des instabilités aérodynamiques et aéroélastiques. La méthodologie proposée repose sur la simulation 2D d'une coupe de tête et met à profit la linéarisation pour analyser la contribution de sources locales en fonction de la fréquence réduite, du diamètre nodal et de la déformée modaleTransonic flows, which are common in aeronautical and spatial propulsion systems, produce shock-waves over solid boundaries. When a shock-wave impacts the boundary layer, an adverse pressure gradient is generated and a thickening or even a separation of the boundary layer is induced. If the solid boundary vibrates, the shock-wave oscillates, interacts with the boundary layer and produce a fluctuation of the static pressure at the wall. This induces an exchange of energy between the fluid and the structure which can be stabilising or lead to an aeroelastic instability (flutter).The main objective of this PhD thesis is the modelling of the unsteady behaviour the simulation of the shock-wave/boundary layer interaction for fluid-structure interaction studies. To this end, simulations have been carried out to solve Reynolds-Averaged Navier-Stokes equations using two equations turbulence model. The method is validated thanks to experimental data obtained on a transonic nozzle dedicated to aeroelastic studies. This method is then use to increase the predictability of flutter events in turbomachinery.A time linearised frequency-domain method is applied to RANS equations. It is shown that the unsteady behaviour of the turbulent boundary-layer contributes to the fluctuating static pressure when the shock-wave boundary layer interaction is strong. Hence, the frozen turbulence assumption is not valid and the turbulence model must be derivated. Thus, the regularisation of the non derivable operators is proposed and applied on k-? Wilcox (2006) turbulence model.The unsteady behaviour of the shock-wave/boundary-layer interaction in a transonic nozzle is evaluated thanks to 2D numerical simulations and shows good agreement with experimental data. When varying the reduced frequency an aeroelastic instability is found, known as transonic flutter. An active control device generating backward travelling pressure waves is then designed and numerically validated.Finally, a methodology is proposed to understand the aerodynamic onsets of transonic flutter. To this end, a preliminary design of a high bypass ratio transonic fan has been carried out. This fan, named ECL5, is dedicated to experimental aerodynamic and aeroelastic studies. The methodology relies on 2D simulations of a tip blade passage and uses linearisation to analyse the contribution of local sources as a function of reduced frequency, nodal diameter and mode shape
16
Sigfrids, Timmy. "Hot wire and PIV studies of transonic turbulent wall-bounded flows." Licentiate thesis, KTH, Mechanics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1577.
Abstract:
The compressible turbulent boundary layer developing over atwo-dimensional bump which leads to a supersonic pocket with aterminating shock wave has been studied. The measurements havebeen made with hot-wire anemometry and Particle ImageVelocimetry (PIV).
A method to calibrate hot-wire probes in compressible ow hasbeen developed which take into account not only the ow velocitybut also the inuence of the Mach number, stagnation temperatureand uid density. The calibration unit consists of a small jetow facility, where the temperature can be varied. The hot wiresare calibrated in the potential core of the free jet. The jetemanates in a container where the static pressure can becontrolled, and thereby the gas density. The calibration methodwas verfied in the at plate zero pressure gradient turbulentboundary layer in front of the bump at three different Machnumbers, namely 0.3, 0.5 and 0.7. The profiles were alsomeasured at different static pressures in order to see theinuence of varying density. Good agreement between the profilesmeasured at different pressures, as well as with the standardlogarithmic profile was obtained.
The PIV measurements of the boundary layer ow in front ofthe 2D bump showed good agreement with the velocity profilesmeasured with hotwire anemometry. The shock wave boundary layerinteraction was investigated for an inlet Mach number of 0.69.A lambda shock wave was seen on the downstream side of thebump. The velocity on both sides of the shock wave as measuredwith the PIV was in good agreement with theory. The shock wavewas found to cause boundary layer separation, which was seen asa rapid growth of the boundary layer thickness downstream theshock. However, no back ow was seen in the PIV-data, probablybecause the seeding did not give enough particles in theseparated region. The PIV data also showed that the shock wavewas oscillating, i.e. it was moving approximately 5 mm back andforth. This distance corresponds to about five boundary layerthicknesses in terms of the boundary layer upstream theshock.
Descriptors:Fluid mechanics, compressible ow,turbulence, boundary layer, hot-wire anemometry, PIV, shockwave boundary layer interaction, shape factor.
17
Ayet, Alex. "Flux de quantité de mouvement à l'interface air-mer : approche théorique du couplage entre turbulence et vagues de vent On the Impact of Long Wind-Waves on Near-Surface Turbulence and Momentum Fluxes, in Boundary-Layer Meteorology volume 174, March 2020 Scalewise return to isotropy in stratified boundary layer flows, in JGR Atmospheres 125 (16), August 2020 Scaling laws for the length scale of energy‐containing eddies in a sheared and thermally stratified atmospheric surface layer, in Geophysical Research Letters 47(23), December 2020." Thesis, Brest, 2020. http://www.theses.fr/2020BRES0038.
Abstract:
Malgré de nombreuses études, le lien de causalité entre vent et vagues fait toujours l’objet de controverses : cela est dû entre autres au caractère multi-échelle d'une surface océanique réaliste, et à la présence de déferlements, qui modifient radicalement sa topologie. Dans cette thèse, ces deux questions sont abordées sous un angle théorique, à travers un modèle phénoménologique, qui relie les propriétés spectrales et moyennées de la turbulence proche de paroi en utilisant la géométrie de tourbillons attachés à celle-ci. La première partie de la thèse revisite ce modèle phénoménologique en questionnant ses hypothèses sous-jacentes et révèle, en particulier, des incohérences dans les modèles utilisés pour décrire le terme de redistribution d'énergie entre composantes turbulentes (modèle de Rotta). Le modèle phénoménologique est ensuite utilisé pour étudier le couplage entre vagues de vent longues (de l'ordre de 10m) et turbulence. Les résultats démontrent que la déformation des tourbillons attachés induite par cette interaction pourrait expliquer une partie de la variabilité des flux de quantité de mouvement à un vent moyen donné. Finalement, le couplage entre la turbulence et les vagues courtes et déferlantes est abordé en définissant une sous-couche rugueuse dans laquelle les propriétés des tourbillons attachés sont définies par la vitesse des fronts déferlants dominants pour un vent donné. Ces deux études posent les bases d'un nouveau paradigme, permettant d'étudier le couplage multi-échelle entre le spectre turbulent et le spectre des vagues. Celui-ci pourrait permettre de mieux prendre en compte l'influence de paramètres environnementaux sur les flux de quantité de mouvement et de chaleur. Il ouvre ainsi de nouvelles perspectives pour les études théoriques et pour l’exploration des données expérimentalesDespite numerous works, the causal link between wind and waves is still a controversial subject. This is due, among others, to the multi-scale nature of a realistic ocean surface and to wave breaking, which changes its topology. In this thesis, such problems are studied from a theoretical perspective, using a phenomenological model linking the spectral and averaged properties of wall-bounded turbulence through the geometry attached eddies.The first part of the thesis revisits this phenomenological model by questioning its underlying assumptions and, in particular, reveals inconsistencies in the models used for the energy redistribution between turbulence components (the Rotta model). The phenomenological model is then used to study the coupling between long wind-waves (of order 10m) and turbulence. Results indicate that the deformation of attached eddies, induced by this interaction, could explain some of the variability in momentum fluxes for a given mean wind. Finally, the study of the coupling between turbulence and short breaking waves is approached by defining a roughness sublayer, in which the properties of the attached eddies depend solely on the speed of the dominant breaking fronts for a given wind. These two studies from the basis of a new paradigm to study the multi-scale coupling between the turbulent and wave spectra. This would allow accounting for the influence of environmental parameters on momentum and heat fluxes, and opens new paths both from a theoretical perspective and for the analysis of experimental data
18
Michel, Guillaume. "Parois et ondes de surface : dissipation, effet Doppler et interactions non linéaires." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEE038/document.
Abstract:
Dans cette thèse, nous étudions comment la présence de parois affecte les ondes de surface. La dissipation associée au mouillage, objet central des premiers chapitres, est abordée expérimentalement. Nous mesurons son évolution avec la taille du ménisque et montrons qu’en mouillage total des non-linéarités apparaissent dès que l’oscillation du ménisque atteint l’épaisseur des couches limites. Dans un deuxième temps, nous quantifions les échanges d’énergie ayant lieu lors de laréflexion d’une onde de surface sur une paroi oscillante, appelés effet Doppler généralisé. Après une mise en évidence expérimentale, une approche théorique les évalue et illustre comment leurs effets cumulatifs peuvent mener à des spectres en compétition avec ceux de la turbulence d’ondes. Finalement, nous traitons les interactions entre paquets d’ondes. En géométrie confinée, nous montrons que des résonances à trois ondes gravitaires sont autorisées. Dépassant la problématique des parois, nous caractérisons les interactions entre ondes gravitaires en milieu infini, puis décrivons les grandes échelles de la turbulence d’ondes capillaireIn this thesis, we study the impact of solid boudaries on surface waves. We first consider the dissipation caused by dynamical wetting. We experimentally show how the damping of surface waves evolves with the size of the meniscus and demonstrate that in perfect wetting it leads to a nonlinear behavior as soon as the meniscus oscillation amplitude compares to the thickness of the boundary layer. Secondly, we investigate energy exchanges through scales occuring when a surface wave reflects on an oscillating wall, the so-called generalized Doppler effect. We evidence the creation of Doppler-shifted waves, compute their amplitudes and illustrate how the continuous bouncing of surface waves on wavemakers may lead to self-similar spectra competing with the ones of wave turbulence. Finally, we focus on nonlinear interaction between surface waves. We prove that gravity waves can undergo triad resonances in confined geometry. Going beyond the consequencies of solid boundaries, we perform experiments on four-wave interactions in the gravity regime and describe large scales in capillary wave turbulence
19
Paskin, Liad. "On the interaction of fast traveling Ocean Waves and the Atmospheric Boundary Layer : A Mechanistic Approach combining Field Measurements and High-fidelity Simulations." Thesis, Ecole centrale de Nantes, 2022. http://www.theses.fr/2022ECDN0012.
Abstract:
Dans les zones côtières, l’industrie de l’énergie éolienne migre vers l’environnement marin, où de vastes espaces sont encore disponibles avec des conditions de vent plus fort et mieux contrôlé. L’environnement marin impose de nouveaux défis à une industrie éolienne pourtant bien établie. Il est impératif de prédire et de décrire avec précision la ressource éolienne en mer afin de concevoir des solutions techniques rentables. L’écoulement concerné est caractérisé par une couche limite atmosphérique (CLA), turbulente, où la dynamique de l’océan modifie considérablement l’écoulement atmosphérique par une capacité thermique plus élevée, et par des interactions vent-vagues complexes, importantes dans des situations assez courantes. Cette thèse passe en revue et étend les connaissances actuelles concernant les interactions vent-vagues dans la partie inférieure de la CLA Marine (CLAM), où elles peuvent être importantespour la caractérisation de la ressource éolienne. La CLAM est étudiée par des expériences physiques et numériques, afin de révéler le rôle des mouvements Induits par les Vagues (IV) transférés de la mer vers l’atmosphère. Grâce à l’utilisation d’expériences physiques et numériques complémentaires, de nouvelles perspectives sur les processus d’interaction vent-vague sont obtenuesIn coastal areas, the wind energy industry migrates to the offshore environment, where huge spaces are still available in stronger and better behaved wind conditions. The offshore environment imposes new challenges to a well established wind energy industry. It is imperative to accurately predict and describe the offshore wind resource in order to design cost efficient solutions. The concerned flow is characterized by a turbulent Atmospheric Boundary Layer (ABL) where the ocean’s dynamics significantly alter the atmospheric flow through higher heat capacity and complex wind-wave interactions important in fairly common situations.So this Thesis reviews and extends the current knowledge regarding Wind-Wave interactions in the lower part of the Marine ABL (MABL), where they are possibly significant in the characterization of the wind resource. The MABL is investigated through physical and numerical experiments, to reveal the role of Wave Induced (WI) motions transferred from the sea into the atmosphere. Thanks to the use of complementary physical and numerical experiments, new insights on the wind-wave interaction processes are obtained
20
Baldy, Serge. "Les mécanismes de génération et de dispersion de bulles provenant du déferlement des vagues : observations, analyse et modèle." Aix-Marseille 2, 1987. http://www.theses.fr/1987AIX22056.
Abstract:
Les travaux presentes dans ce memoire ont pour principal objectif: contribuer a l'evaluation des transferts ocean-atmosphere induits par les bulles, par l'etude des mecanismes de generation et de dispersion de bulles provenant du deferlement des vagues. L'essentiel des travaux est constitue par le developpement d'une methode de mesure de bulles, l'obtention et l'analyse de resultats experimentaux sur les populations de bulles generees par le deferlement des vagues et le developpement d'un modele theorique concernant les processus de generation et de dispersion des bulles par un champ de vagues deferlantes. Methode de mesure basee sur l'analyse des intensites diffusees produites par le passage d'une bulle dans un faisceau laser. Cette methode permet d'obtenir directement la probabilite de densite de concentration des bulles en fonction de leur diametre, ainsi que divers parametres complementaires. Les populations de bulles correspondant a differents champs de vagues generes dans la grande soufflerie de simulation des echanges ocean-atmosphere de l'i. M. S. T. Ont ete determinees a differents niveaux, soit en dessous du creux des vagues soit entre le creux et la crete des vagues. Les resultats obtenus sur la concentration, le groupement et la vitesse des bulles permettent l'identification de deux zones: une zone de generation pres de la surface et sur une zone de dispersion en dessous. Le modele theorique propose prend en compte le processus d'injection des bulles en profondeur et l'incorpore, sous la forme d'un terme source, a une equation de dispersion des bulles. Un raisonnement de similitude, comparable a celui utilise dans la theorie de la zone inertielle de kolmogorov, permet de determiner ce terme source. La comptabilite des donnees experimentales disponibles avec les resultats theoriques obtenus parait confirmer la validite du modele propose
21
Bonnifet, Valentin. "Prédiction du phénomène de tremblement sur un profil d'aile avec une approche LES de type PANS-RSM." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS389.
Abstract:
L'objectif de cette étude est le developpement d'un modèle de sous-maille à équations de transport pour la simulation aux grandes échelles. Le modèle de sous-maille est développé par analogie avec le modèle statistique du second ordre proposé par Gerolymos-Lo-Vallet-Younis. Un paramètre de contrôle constant y est introduit afin de régler la quantité d'énergie cinétique turbulente modélisée par le modèle de sous-maille. Ce paramètre permet un passage continue entre la résolution directe et statistique des équations de Navier-Stokes. Cette approche à la capacité de prédire correctement des écoulements turbulents avec un maillage spatio-temporel plus grossier qu'avec l'approche de la simulation au grandes échelles classique utilisant des modèles de sous-maille algébriques. La méthode proposée est utilisée pour simuler un écoulement transsonique autour du profil d'aile OAT15A. Pour les conditions d'entrées étudiées, cet écoulement est le siège d'une interaction onde de choc couche limite turbulente sur l'extrados du profil d'aile provoquant une oscillation auto-entretenue de la position de l'onde de choc. Les résultats montrent que l'approche développée est apte à reproduire le mouvement de l'onde de choc. Une analyse des grandeurs filtrées de l'écoulement, des corrélations turbulentes ainsi que de l'impact du paramètre de contrôle est présentée. Enfin, cette étude énonce des suggestions de développement pour améliorer le modèle de sous-maille proposé en utilisant un paramètre de contrôle inhomogène en espace et/ou en tempsThis PhD was devoted to develop a Large Eddy Simulation subgrid scale model based on transport equations. The subgrid scale model is built in the same manner as second order statistical model suggested by Gerolymos-Lo-Vallet-Younis. A constant control parameter has been introduced to tune the amount of turbulent kinetic energy handled by subgrid scale model. This parameter allows a bridging from Direct Numerical Simulation to Reynolds Averaged Navier-Stokes. This approach can correctly predict turbulent flow with coarser grid and time step than canonical Large Eddy Simulation based on algebraic subgrid scale models where subgrid length scale corresponds to Taylor micro scale. Indeed, the subgrid scale model handles a large part of turbulent kinetic energy in the boundary layer.Transonic flow simulation around OAT15A airfoil is carried out using the suggested approach. On particular inflow conditions, the shock-wave shows a self-sustained motion on the airfoil upper side resulting from the shock-wave boundary layer interaction. Reynolds Averaged Navier-Stokes is not able to predict averaged field because this large unsteadiness is undeterministic and an LES approach is needed. According to the results, the suggested approach can handle shock-wave motion. Filtered flow field, turbulent correlation and control parameter impact analysis are presented. Finally, development ways are suggested in order to improve the subgrid scale model using inhomogeneous control parameter in space and/or time
22
Grossi, Fernando. "Physique et modélisation d’interactions instationnaires onde de choc/couche limite autour de profils d’aile transsoniques par simulation numérique." Thesis, Toulouse, INPT, 2014. http://www.theses.fr/2014INPT0015/document.
Abstract:
L’interaction onde de choc/couche limite en écoulement transsonique autour de profils aérodynamiques est étudiée numériquement utilisant différentes classes de modélisation de la turbulence. Les approches utilisées sont celles de modèles URANS et de méthodes hybrides RANS-LES. L’emploi d’une correction de compressibilité pour les fermetures à une équation est aussi évalué. Premièrement, la séparation intermittente induite par le choc sur un profil supercritique en conditions d’incidence proches de l’angle critique d’apparition du tremblement est analysée. Suite à des simulations URANS, la modélisation statistique la mieux adaptée est étudiée et utilisée dans l’approche DDES (Delayed Detached-Eddy Simulation). L’étude de la topologie de l’écoulement, des pressions pariétales et champs de vitesse statistiques montrent que les principales caractéristiques de l’oscillation auto-entretenue du choc sont capturées par les simulations. De plus, la DDES prédit des fluctuations secondaires de l’écoulement qui n’apparaissent pas en URANS. L’étude de l’interface instationnaire RANS-LES montre que la DDES évite le MSD (modeled stress depletion) pour les phases de l’écoulement attaché ou séparé. Le problème de la ‘zone grise’ et de son influence sur les résultats est considéré. Les conclusions de l’étude sur le profil supercritique est ensuite appliquées à l’étude numérique d’un profil transsonique laminaire. Dans ce contexte, l’effet de la position de la transition de la couche limite sur les caractéristiques de deux régimes d’interaction choc/couche limite sélectionnés est étudié. En conditions de tremblement, les simulations montrent une forte influence du point de transition sur l’amplitude du mouvement du choc et sur l’instationnarité globale de l’écoulementShock wave/boundary layer interactions arising in the transonic flow over airfoils are studied numerically using different levels of turbulence modeling. The simulations employ standard URANS models suitable for aerodynamics and hybrid RANS-LES methods. The use of a compressibility correction for one-equation closures is also considered. First, the intermittent shock-induced separation occurring over a supercritical airfoil at an angle of attack close to the buffet onset boundary is investigated. After a set of URANS computations, a scale-resolving simulation is performed using the best statistical approach in the context of a Delayed Detached-Eddy Simulation (DDES). The analysis of the flow topology and of the statistical wall-pressure distributions and velocity fields show that the main features of the self-sustained shock-wave oscillation are predicted by the simulations. The DDES also captures secondary flow fluctuations which are not predicted by URANS. An examination of the unsteady RANS-LES interface shows that the DDES successfully prevents modeled-stress depletion whether the flow is attached or separated. The gray area issue and its impact on the results are also addressed. The conclusions from the supercritical airfoil simulations are then applied to the numerical study of a laminar transonic profile. Following a preliminary characterization of the airfoil aerodynamics, the effect of the boundary layer transition location on the properties of two selected shock wave/boundary layer interaction regimes is assessed. In transonic buffet conditions, the simulations indicate a strong dependence of the shock-wave motion amplitude and of the global flow unsteadiness on the tripping location
23
Gaurier, Benoît. "Etude expérimentale des performances d'une hydrolienne, soumise aux effets de la turbulence et de l'intéraction houle-courant." Thesis, Normandie, 2020. http://www.theses.fr/2020NORMLH11.
Abstract:
Dans le contexte actuel du réchauffement climatique, l’extraction de l’énergie des courants marins par des hydroliennes se doit d’intégrer le mix énergétique de demain. Ces machines étant confrontées à un environnement marin difficile, il est nécessaire de connaître leur comportement dans des conditions de fonctionnement réaliste pour garantir une utilisation optimale. Dans ces travaux, les performances d’une hydrolienne sont étudiées, quand la machine est soumise à un courant turbulent ou aux effets combinés de la houle et du courant. La représentation physique des essais à échelle réduite est d’abord abordée, en se focalisant sur la caractérisation de l’écoulement incident et ses effets sur une maquette d’hydrolienne à l’échelle 1/20. La position et le type de mesure de la vitesse amont sont discutés afin de définir avec précision ses performances et sa réponse temporelle et spectrale. Ces éléments sont essentiels dans la définition des standards de certification des modélisations expérimentales. La représentation de variations bathymétriques permet de générer des écoulements turbulents, caractérisés par le passage de structures tourbillonnaires de la taille du rotor. La réponse de la machine est déterminée de manière globale et locale, pour plusieurs positions relatives de la machine par rapport aux obstacles. Les effets combinés de la houle et du courant sur le comportement de la machine sont étudiés à partir de résultats de mesures obtenues dans trois infrastructures d’essais. Des différences significatives entre les bassins apparaissent et une discussion sur leur origine est menéeIn the context of global warming, the extraction of energy by tidal turbines from marine currents must be integrated into the future energetic mix. Being confronted with a difficult marine environment, it is required to know the turbines’ behaviour when they are submitted to realistic solicitations to guarantee an optimal use. In this work, the marine turbine performance is studied when the machine is submitted to a turbulent current or a combined wave-current effect. The physical representation of trials at reduced scale is first described focusing on the incoming flow characterisation and its effects on a turbine model at 1:20 scale. The locationand measurement type of the upstream velocity are discussed to accurately define its performance and its temporal and spectral response. Such parameters are essential in the definition of certification standards for experimental modelling. The bathymetric variation representation enables turbulent flow to be generated. They are mainly characterized by large eddies with a size corresponding to the rotor. The turbine response is determined in a global and local way for many relative turbine locations versus the obstacles. The combined wave and current effects on the turbine behaviour are studied from measurement results carried out in three facilities. Significant differences between the tanks appear and a discussion on their origin is proposed
24
Solakoglu, Erhan. "Modélisation des écoulements compressibles turbulents. Interaction onde de choc/couche limite turbulente." Rouen, 1994. http://www.theses.fr/1994ROUES023.
Abstract:
Le travail présenté dans ce mémoire est consacré à la modélisation de la turbulence, étudiée dans le cadre particulier de la simulation d'interactions onde de choc/couche limite. Les cas-tests étudiés sont: canal transsonique 2D avec bosse à la paroi, écoulement supersonique 2D sur une marche montante et canal transsonique 3D avec bosse en flèche. Les modèles de turbulence utilisés sont: modèle algébrique de Baldwin-Lomax et modèle k-epsilon de Jones-Launder. Une revue bibliographique fait l'objet du premier chapitre. Le deuxième chapitre développe des équations de Navier-Stokes, moyennées au sens de Favre. Le problème de la fermeture des équations moyennées et les différents modèles de turbulence sont présentés dans le troisième chapitre. Dans le quatrième chapitre, la méthode numérique prédicteur-correcteur de Maccormack, implicite et volumes finis, est détaillée. L'exploitation et l'analyse des résultats numériques constituent le cinquième chapitre. Le dernier chapitre est consacré aux conclusions et perspectives
25
Badr, Mohammad Ali. "Shock wave turbulent boundary layer interaction over a protrusion." Thesis, Wichita State University, 2011. http://hdl.handle.net/10057/3942.
Abstract:
This research attempts to investigate an important and common phenomenon in
aerodynamics called shock interaction in a turbulent flow’s boundary layer. Due to advancements
in current computational units, more complex geometries could be simulated with providing
more accurate results. The tools used in this investigation are computational turbulent model of
hybrid RANS/LES, called detached eddy simulation (DES). DES and its variant delayed
detached eddy simulation (DDES) were the two computational schemes used for numerical
simulation. Two protrusions were focused on in this work: a symmetrical bump and a proposed
aircraft UHF antenna. Computation where performed with commercial software Cobalt and
FLUENT in the High Performance Computing Center (HiPeCC) in Wichita State University.
Computational simulation is costly in terms of energy consumption and time usage. Even so with
the advanced computational units of HiPeCC, using in average of 18 processors, total simulation
for this research took over 2 months of simulation.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering
26
Nielson, Kevin Derek. "Analysis and gyrokinetic simulation of MHD Alfvén wave interactions." Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/3504.
Abstract:
The study of low-frequency turbulence in magnetized plasmas is a difficult problem due to both the enormous range of scales involved and the variety of physics encompassed over this range. Much of the progress that has been made in turbulence theory is based upon a result from incompressible magnetohydrodynamics (MHD), in which energy is only transferred from large scales to small via the collision of Alfv ́n waves propagating oppositely along the mean magnetic field. Improvements in laboratory devices and satellite measurements have demonstrated that, while theories based on this premise are useful over inertial ranges, describing turbulence at scales that approach particle gyroscales requires new theory.
In this thesis, we examine the limits of incompressible MHD theory in describing collisions between pairs of Alfvén waves. This interaction represents the fundamental unit of plasma turbulence. To study this interaction, we develop an analytic theory describing the nonlinear evolution of interacting Alfv ́n waves and compare this theory to simulations performed using the gyrokinetic code AstroGK. Gyrokinetics captures a much richer set of physics than that described by incompressible MHD, and is well-suited to describing Alfvénic turbulence around the ion gyroscale. We demonstrate that AstroGK is well suited to the study of physical Alfvén waves by reproducing laboratory Alfvén dispersion data collected using the LAPD. Additionally, we have developed an initialization alogrithm for use with AstroGK that allows exact Alfvén eigenmodes to be initialized with user specified amplitudes and phases.
We demonstrate that our analytic theory based upon incompressible MHD gives excellent agreement with gyrokinetic simulations for weakly turbulent collisions in the limit that k⊥ ρi << 1. In this limit, agreement is observed in the time evolution of nonlinear products, and in the strength of nonlinear interaction with respect to polarization and scale. We also examine the effect of wave amplitude upon the validity of our analytic solution, exploring the nature of strong turbulence. In the kinetic limit where k⊥ ρi ≥ 1 where incompressible MHD is no longer a valid description, we illustrate how the nonlinear evolution departs from our analytic expression.
The analytic theory we develop provides a framework from which more sophisticated of weak and strong inertial-range turbulence theories may be developed. Characterization of the limits of this theory may provide guidance in the development of kinetic Alfvén wave turbulence.
27
Ben, Hassan Saïdi Ismaïl. "Numerical simulations of the shock wave-boundary layer interactions." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS390/document.
Abstract:
Les situations dans lesquelles une onde de choc interagit avec une couche limite sont nombreuses dans les industries aéronautiques et spatiales. Sous certaines conditions (nombre de Mach élevé, grand angle de choc…), ces interactions entrainent un décollement de la couche limite. Des études antérieures ont montré que la zone de recirculation et le choc réfléchi sont tous deux soumis à un mouvement d'oscillation longitudinale à basse fréquence connu sous le nom d’instabilité de l’interaction onde de choc / couche limite (IOCCL). Ce phénomène appelé soumet les structures à des chargement oscillants à basse fréquence qui peuvent endommager les structures.L’objectif du travail de thèse est de réaliser des simulations instationnaires de l’IOCCL afin de contribuer à une meilleure compréhension de l’instabilité de l’IOCCL et des mécanismes physiques sous-jacents.Pour effectuer cette étude, une approche numérique originale est utilisée. Un schéma « One step » volume fini qui couple l’espace et le temps, repose sur une discrétisation des flux convectifs par le schéma OSMP développé jusqu’à l’ordre 7 en temps et en espace. Les flux visqueux sont discrétisés en utilisant un schéma aux différences finies centré standard. Une contrainte de préservation de la monotonie (MP) est utilisée pour la capture de choc. La validation de cette approche démontre sa capacité à calculer les écoulements turbulents et la grande efficacité de la procédure MP pour capturer les ondes de choc sans dégrader la solution pour un surcoût négligeable. Il est également montré que l’ordre le plus élevé du schéma OSMP testé représente le meilleur compromis précision / temps de calcul. De plus un ordre de discrétisation des flux visqueux supérieur à 2 semble avoir une influence négligeable sur la solution pour les nombres de Reynolds relativement élevés considérés.En simulant un cas d’IOCCL 3D avec une couche limite incidente laminaire, l’influence des structures turbulentes de la couche limite sur l’instabilité de l’IOCCL est supprimée. Dans ce cas, l’unique cause d’IOCCL suspectée est liée à la dynamique de la zone de recirculation. Les résultats montrent que seul le choc de rattachement oscille aux fréquences caractéristiques de la respiration basse fréquence du bulbe de recirculation. Le point de séparation ainsi que le choc réfléchi ont une position fixe. Cela montre que dans cette configuration, l’instabilité de l’IOCCL n’a pas été reproduite.Afin de reproduire l’instabilité de l’IOCCL, la simulation de l’interaction entre une onde de choc et une couche limite turbulente est réalisée. Une méthode de turbulence synthétique (Synthetic Eddy Method - SEM) est développée et utilisée à l’entrée du domaine de calcul pour initier une couche limite turbulente à moindre coût. L’analyse des résultats est effectuée en utilisant notamment la méthode snapshot-POD (Proper Orthogonal Decomposition). Pour cette simulation, l’instabilité de l’IOCCL a été reproduite. Les résultats suggèrent que la dynamique du bulbe de recirculation est dominée par une respiration à moyenne fréquence. Ces cycles successifs de remplissage / vidange de la zone séparée sont irréguliers dans le temps avec une taille maximale du bulbe de recirculation variant d’un cycle à l’autre. Ce comportement du bulbe de recirculation traduit une modulation basse fréquence des amplitudes des oscillations des points de séparation et de recollement et donc une respiration basse fréquence de la zone séparée. Ces résultats suggèrent que l’instabilité de l’IOCCL est liée à cette dynamique basse fréquence du bulbe de recirculation, les oscillations du pied du choc réfléchi étant en phase avec le point de séparationSituations where an incident shock wave impinges upon a boundary layer are common in the aeronautical and spatial industries. Under certain circumstances (High Mach number, large shock angle...), the interaction between an incident shock wave and a boundary layer may create an unsteady separation bubble. This bubble, as well as the subsequent reflected shock wave, are known to oscillate in a low-frequency streamwise motion. This phenomenon, called the unsteadiness of the shock wave boundary layer interaction (SWBLI), subjects structures to oscillating loads that can lead to damages for the solid structure integrity.The aim of the present work is the unsteady numerical simulation of (SWBLI) in order to contribute to a better understanding of the SWBLI unsteadiness and the physical mechanism causing these low frequency oscillations of the interaction zone.To perform this study, an original numerical approach is used. The one step Finite Volume approach relies on the discretization of the convective fluxes of the Navier Stokes equations using the OSMP scheme developed up to the 7-th order both in space and time, the viscous fluxes being discretized using a standard centered Finite-Difference scheme. A Monotonicity-Preserving (MP) constraint is employed as a shock capturing procedure. The validation of this approach demonstrates the correct accuracy of the OSMP scheme to predict turbulent features and the great efficiency of the MP procedure to capture discontinuities without spoiling the solution and with an almost negligible additional cost. It is also shown that the use of the highest order tested of the OSMP scheme is relevant in term of simulation time and accuracy compromise. Moreover, an order of accuracy higher than 2-nd order for approximating the diffusive fluxes seems to have a negligible influence on the solution for such relatively high Reynolds numbers.By simulating the 3D unsteady interaction between a laminar boundary layer and an incident shock wave, we suppress the suspected influence of the large turbulent structures of the boundary layer on the SWBLI unsteadiness, the only remaining suspected cause of unsteadiness being the dynamics of the separation bubble. Results show that only the reattachment point oscillates at low frequencies characteristic of the breathing of the separation bubble. The separation point of the recirculation bubble and the foot of the reflected shock wave have a fixed location along the flat plate with respect to time. It shows that, in this configuration, the SWBLI unsteadiness is not observed.In order to reproduce and analyse the SWBLI unsteadiness, the simulation of a shock wave turbulent boundary layer interaction (SWTBLI) is performed. A Synthetic Eddy Method (SEM), adapted to compressible flows, has been developed and used at the inlet of the simulation domain for initiating the turbulent boundary layer without prohibitive additional computational costs. Analyses of the results are performed using, among others, the snapshot Proper Orthogonal Decomposition (POD) technique. For this simulation, the SWBLI unsteadiness has been observed. Results suggest that the dominant flapping mode of the recirculation bubble occurs at medium frequency. These cycles of successive enlargement and shrinkage of the separated zone are shown to be irregular in time, the maximum size of the recirculation bubble being submitted to discrepancies between successive cycles. This behaviour of the separation bubble is responsible for a low frequency temporal modulation of the amplitude of the separation and reattachment point motions and thus for the low frequency breathing of the separation bubble. These results tend to suggest that the SWBLI unsteadiness is related to this low frequency dynamics of the recirculation bubble; the oscillations of the reflected shocks foot being in phase with the motion of the separation point
28
Richardson, G. A. "Algebraic stress modelling for shock-wave/turbulent boundary-layer interactions." Thesis, Cranfield University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267213.
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Silva, Freire Atila P. "An asymptotic approach for shock-wave/turbulent boundary layer interactions." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.330307.
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Labreuche, Pierre. "Ondes de relief dans l'océan profond : mélange diapycnal et interactions avec les oscillations inertielles." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAU035/document.
Abstract:
L'Océan Austral est une zone clef pour la circulation océanique tant à cause de l'intensité du courant circumpolaire antarctique qu'en tant que région de formation des masses d'eaux abyssales de l'océan global. Pour modéliser l'océan et prévoir les changements climatiques futurs, il est important de comprendre les processus de mélange diapycnal qui lient ces eaux abyssales aux couches supérieures. Dans l'Océan Austral, des courants profonds et intenses s'écoulent sur une topographie accidentée, ce qui génère des ondes internes de relief très énergétiques. Actuellement, la dissipation de l'énergie induite par ces ondes de relief est la candidate principale pour expliquer les forts taux de mélange observés à ces latitudes. L'objet du présent travail de thèse est de comprendre comment les ondes internes de relief sont dissipées et affectent la circulation et le mélange diapycnal dans l'océan abyssal. Nous examinons l'impact de ces ondes sur le mélange profond au moyen d'une combinaison d'expertise de terrain, de simulations non hydrostatiques bi-dimensionnelles et de calculs théoriques. Sur la gamme de paramètres étudiés, nous montrons, en présence des ondes de relief, une intensification du taux de dissipation d'énergie cinétique turbulente sur une profondeur de 1000 m au-dessus de la topographie, atteignant typiquement ~20 mW/m2. Nous montrons également comment les ondes participent à des interactions triadiques impliquant des oscillations inertielles qui sont amplifiées par intéractions résonantes contrôlées par les ondes de relief. Finalement, nous préparons de futures études tri-dimensionnelles en concevant un cadre numérique et en décrivant des outils théoriques adaptés à ce problème. Nos résultats préliminaires en trois dimensions montrent qui le confinement méridien de la topographie réduit significativement l'émissions d'ondes internes de reliefThe Southern Ocean plays a key role in global ocean circulation by connecting the major ocean basins with the intense Antarctic Circumpolar Current and as a formation region for abyssal water masses of the global ocean. Understanding the diapycnal mixing processes that link these abyssal waters to the overlying layers is essential both for ocean modelling and for predicting future climate change. In the Southern Ocean, deep reaching currents impinge on rough topography and create highly energetic internal lee waves. The dissipation of the energy of these internal lee waves is the main candidate for explaining the high mixing rates between waters of different densities observed at these latitudes. The purpose of this study is to understand the fate of the internal lee wave energy and how it affects the circulation and diapycnal mixing in the abyssal ocean. We first study the impact of internal lee waves on deep mixing with the combination of field expertise, two-dimensional non hydrostatic numerical simulations and theoretical developments. Over the range of parameters studied, an enhanced bottom turbulent kinetic energy dissipation is observed in the bottom 1000 m, typically reaching $sim$ 20 mW.m$^{-2}$. We further show that internal lee waves undergo non-dissipative wave-wave interactions that can be rationalized as resonant triad interactions between the bottom emitted internal lee waves, inertial oscillations and linear combinations of these two waves. We then build a three-dimensional model configuration and specific diagnostic methods that pave the way for future investigations in three dimensions. Preliminary results with the three-dimensional numerical configuration show that the meridional confinement of the topography notably reduces the emission of internal lee waves
31
Cahen, Juliette. "Modélisation de la turbulence pour la prédiction d'écoulements internes compressibles. Validation d'un modèle (k,epsilon) en configuration tridimensionnelle d'interaction onde de choc-couche limite turbulente." Rouen, 1993. http://www.theses.fr/1993ROUES022.
Abstract:
Ce mémoire relate un travail consacré à la modélisation de la turbulence, étudiée dans le cadre particulier de la simulation d'interactions onde de choc-couche limite turbulente. Dans une première partie, une revue des différents types de modèles est effectuée selon une hiérarchie allant des modèles les plus simples, basés sur la détermination d'une longueur de mélange, à des modèles plus complexes prenant en compte les caractères anisotrope et tridimensionnel de la turbulence. La seconde partie de ce mémoire est consacrée à la mise en œuvre et à la validation d'un modèle de turbulence à deux équations de transport (k, epsilon) de Jones-Launder en formulation bas nombre de Reynolds. On présente l'intégration de ce modèle dans un code de calcul tridimensionnel, Canari, résolvant les équations de Navier-Stokes moyennées. Ce code de calcul est caractérisé par une méthode numérique fondée sur une approche volumes finis utilisant un schéma explicite centré de type Lax-Wendroff. Un travail d'implantation d'un modèle du second ordre de type ASM dont le code est également considéré. La validation est effectuée sur différents cas expérimentés d'écoulements internes transsoniques. On présente une analyse particulièrement détaillée d'un cas d'interaction onde de choc-couche limite fortement tridimensionnelle pour laquelle on dispose de nombreuses données expérimentales pour le champ moyen et le champ turbulent. Les résultats obtenus avec le modèle (k, epsilon) sont également comparés avec ceux obtenus en utilisant un modèle de longueur de mélange initialement développé dans le code. Ces comparaisons mettent en évidence la nette amélioration apportée par l'utilisation du modèle (k, epsilon), notamment dans les régions où l'écoulement est fortement décollé
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Coronado, Domenge Patricia X. "Delayed-Detached-Eddy Simulation of Shock Wave/Turbulent Boundary Layer Interaction." Scholarly Repository, 2009. http://scholarlyrepository.miami.edu/oa_theses/220.
Abstract:
The purpose of this thesis is to study the shock/wave turbulent boundary layer interaction by using delayed-detached-eddy simulation (DDES) model with a low diffusion E-CUSP (LDE) scheme with fifth-order WENO scheme. The results show that DDES simulation provides improved results for the shock wave/turbulent boundary layer interaction compared to those of its predecessor the detached-eddy simulation (DES). The computation of mesh refinement indicates that the grid density has significant effects on the results of DES, while being resolved by applying DDES simulation. Spalart in 1997 developed the Detached-Eddy Simulation (DES) model, which is a hybrid RANS and LES method, to overcome the intensive CPU requirement from LES models. Near the solid surface within a wall boundary layer, the unsteady RANS model is realized. Away from the wall surface, the model automatically converts to LES. The Delayed-Detached-Eddy Simulation (DDES) was suggested by Spalart in 2006 to improve the DES model previously developed. The transition from the RANS model to LES in DES is not grid spacing independent, therefore a blending function is introduced to the recently developed DDES model to make the transition from RANS to LES grid spacing independent. The DDES is validated by computing a 3D subsonic flat plate turbulent boundary layer. The first case studied using DDES is a 3D transonic channel with shock/turbulent boundary layer interaction. It consists of two straight side walls, a straight top wall, and a varying shape in span-wise direction for a bottom wall. The second case studied consists of a 3D transonic inlet-diffuser. Both results are compared with experimental data. The computed results of the transonic channel agree well with experimental data.
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Kakollu, Satyanarayana. "Numerical simulation of strong turbulence over water waves." Master's thesis, Mississippi State : Mississippi State University, 2003. http://library.msstate.edu/etd/show.asp?etd=etd-12112002-125436.
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Casagrande, Vanessa. "Synchronization, waves, and turbulence in systems of interacting chemical oscillators." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=979660319.
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Murray, Neil Paul. "Three-dimensional turbulent shock-wave : boundary-layer interactions in hypersonic flows." Thesis, Imperial College London, 2007. http://hdl.handle.net/10044/1/7963.
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Salin, Andrea. "Numerical modelling of swept and crossing shock-wave turbulent boundary-layer interactions." Thesis, Kingston University, 2014. http://eprints.kingston.ac.uk/29992/.
Abstract:
Two configurations that have received a great deal of attention in the last decades are namely the single-fin and double-fin. In these interactions, deflected un-swept sharp fins are used to generate single-swept and double-crossing oblique shock-waves that interact with a supersonic/hypersonic turbulent boundary-layer developing over a flat plate. Following the swept-shock interaction, the study of crossing-shock interaction represents a logical progression in the general study of shock- wave / turbulent boundary-layer interactions (SWTBLIS). These rather simple geometries allow isolating the inherent flow physics which can be applied to more complex configurations. Besides having fundamental importance, swept- and crossing-shock interactions also have important engineering applications. Research findings on single-fin can be applied, for example, in the design of wing/tail fuselage juncture, and in high incidence flows on swept delta wings and slender bodies. The double-fin, on the other hand, could represent a simplification of a high-speed inlet of vehicles employing air-breathing propulsion. Such an inlet geometry concepts employ side- wall compression to increase, in reasonable short distance, the air pressure prior combustion. The side-wall compression surfaces (i.e. fins) generate an oblique shock-wave that crosses one another and interacts with the boundary-layer developing on the windward of the fiJselage. The nature of such complex 3-D interactions can affect the performance of the inlet as well as the engine. If the physical principles governing these interactions are well determined and understood, then an active control system can be developed so that to reduce the risk of engine fail and optimise its performance. Note that the findings of this investigation are crucial for the design of effective thermal protection systems since these interactions produce high peaks of heating which can damage materials severely around concentrated areas where shock-waves hit surfaces. The main objective of this thesis is to predict accurately secondary separation flows and wall heat transfer under conditions of turbulent and separated flow, which has represented a challenging problem for computational fluid dynamists for the past thirty years. Steady RANS modelling has been carried out for a symmetrical double-sharp-fin configuration with an inclination angles from 7 degrees to 21 degrees, Mach 3.92 and Reynolds number RC5 = 3.08X105, aiming for comparison and improvement of wall heat transfer predictions. Grid refinement and turbulence modelling studies have been carried out carefully in order to improve previous numerical predictions against experimental measurements. Overall, current steady Reynolds Averaged Navier-Stokes computations with co-based Reynolds Stress Model (RANS-RSM) outperformed one- and two-equation conventional turbulence models as well as other numerical investigations carried out over the last three decades. My original contribution to knowledge focuses primarily on improving numerical prediction of wall heat transfer in supersonic/hypersonic side-wall compression inlets and deflected aerodynamic surfaces. Different methods of evaluation of the wall heat transfer, to improve the comparison with available experiments, have been proposed for both single- and double-fin configurations. Results are compared with experimental measurements and previous numerical studies. The most challenging numerical prediction of wall heat transfer coefficient in strong pressure gradient flows has been largely improved, for the first time, by adopting three approaches: (1) choosing a suitable turbulence model - the wall heat transfer coefficients peaks computed by RANS-RSM are in fact closer to experimental peaks (50% improvement) in comparison with other conventional two- equation eddy-viscosity turbulence models; (2) increasing the wall turbulent Prandtl number in region of high shear strain; (3) and finally, adopting a pressure-based correlation formula. The latter appeared to be the most effective method of predicting wall heat transfer coefficient, provided accurate wall pressure distributions being obtained by numerical simulations. Within the scope of this original research, complex flow structures are also numerically investigated in detail to verify and further examine, existing conclusions on the nature of incipient and secondary separation evolution at monotonic increasing shock strengths, for the single-fin configurations at Mach numbers 3, 4 and 5 and at beta fin’s deflection angles [if ranging from 9 degrees to 30.6 degrees. The nature of secondary separation will be explained at different regimes III-VI in condition of subsonic and supersonic transverse conical cross-flow. Computational Fluid Dynamics (CFD) analyses using conventional two-equation turbulence models are unable to capture secondary flow separations at moderate interaction strength - a phenomenon observed in experiments and believed to be associated with a ‘weakly-turbulent’ boundary-layer separation. I investigated this aspect in further details. In fact, RANS-RSM, due to its capability of reproducing correct level of turbulence kinetic energy (TKE), confirmed the presence of such a ‘weakly-turbulent’ state of transverse cross-flow in the near-wall regions underneath the main cross-flow vortex at moderate interaction strength (regime 111/] V). Computations revealed that the development of the secondary separation at early stage (regime III) is caused by the interaction of (1) the ‘conically-subsonic’ (Mn < 1) flow region of the transverse cross-flow developed from the primary reattachment (R[sub 1]) line with (2) the subsonic (M < 1) region of the near-wall secondary cross-flow which forms within the primary separation zone. Turbulence behaviour was also analysed, for the first time, in the reverse cross-flow in order to investigate the influence of the (laminar or turbulent) flow state in evolution of secondary separation phenomenon at increasing shock strengths. Remarkably, computed results are in good agreement with the conclusions of experimentalists. In fact, the secondary separation (S[sub 2]) cross- flow gradually disappears in transitional (laminar-to-turbulent) supersonic conical cross-flow regions (regimes IV and V), except at the regime VI, where S[sub 2] reappears, accompanied by a secondary reattachment (R[sub 2]) line, once the supersonic conical cross-flow becomes fully-developed turbulent. At this stage, the embedded normal shock-wave reaches the critical shock strength (xi[sub i]- 1.56) which is typically required to force turbulent separation. This study demonstrated numerically that the critical value xi[sub i]= 1.5 corresponds to the incipient secondary separation condition which is typical for the separated turbulent flows (regime V). A careful quantitative and qualitative analysis on the developments of the turbulence kinetic energy across the 3-D domain excitingly also confirms these findings. Thus, it was concluded that evolution of the secondary separation phenomenon at increasing shock strengths is influenced not only by the acceleration of the transverse cross-flow to conically-supersonic regime but also by some physical mechanisms that amplify the turbulence levels in the near-wall reverse cross-flow. One unique feature of the crossing-shock interaction at regime III; i.e. the secondary separation phenomenon, initially observed in the single-fin flow, has been successfully reproduced in a double-fin configuration by numerical computation using RANS-RSM. CFD predicted 3-D flow stream-surfaces showed that the initially weak secondary separation has been further strengthened in span-wise direction towards the central separated zone. Additional flow topology at stronger crossing-shock interactions has been also presented showing the evolution of surface flow-pattems at increasing shock strengths. To the author’s knowledge, the present study represents the first attempt to predict the evolution of secondary separation phenomenon in single- and double-fin configurations at different interaction regimes. Findings suggest that the classification originally made by Zheltovodov er al. for single- fin flows (hence for Swept-Shock-Wave/Turbulent Boundary-Layer Interaction, S-SWTBLI) can be also applied to double-fin configurations (thus for Crossing-Shock-Wave/Turbulent Boundary- Layer Interaction, C-SWTBLI).
37
Yang, Wei-Li. "Numerical simulation of a shock wave/turbulent boundary layer interaction in a duct." Case Western Reserve University School of Graduate Studies / OhioLINK, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=case1056382899.
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Mezemate, Yacine. "Analyse et modélisation multifractales des interactions ondes-turbulence-biologie dans un lac urbain." Thesis, Paris Est, 2014. http://www.theses.fr/2014PEST1166/document.
Abstract:
Les recherches en milieu lacustre ont généralement porté sur les grands lacs naturels et les barrages. Or les défis scientifiques que présentent les lacs urbains sont nombreux du fait de leur faible profondeur et de leur extension .Le travail que nous présentons ici s'inscrit dans le cadre du projet Petits Lacs Urbains Mesures Modèles Multi-Echelles (PLUMMME), projet financé par la région Île-de-France (programme DIM R2DS).Ce projet a permis l'équipement du lac de Créteil en mesures à haute résolution. Ce sont ces mesures physiques et biologiques qui sont essentiellement exploitées dans cette thèse, parfois en comparaison avec celles du lac du Bourget. La première étape de cette thèse a été ainsi d'enrichir la base de données déjà disponible. Pour cela, nous avons mis en place une station de mesure en continu (capteurs de température, chlorophylle et luminosité, données météorologique telles que vitesse du vent et température atmosphérique), ainsi que deux chaînes de mesures comportant différents capteurs. Des campagnes de mesures spécifiques ont également été réalisées pour l'étude de hydrodynamique à l'aide d'un courantomètre de type Acoustic Doppler Velocimeter (ADV), ainsi qu'un profileur de type Acoustic Doppler Current Profilers (ADCP) à deux points différents du lac (point central et point du rejet d'eaux pluviales). L'analyse des différents champs montre que le lac présente des stratifications avec une période d'une semaine. Nous avons également identifié les modes d'oscillations des ondes internes lorsque ces dernières se produisent sous l'effet du vent. L'analyse spectrale a permis de mettre en évidence une première propriété d'invariance d'échelle des différents champs mesurés. Les différents processus physique (turbulence, stratification, écoulement proche de la paroi) opérant le long de la colonne d'eau ont également été caractérisés. L'analyse spectrale ne permet pas de mettre en évidence le caractère intermittent des fluctuations des champs mesurés, ces dernières peuvent par contre être analysées à l'aide des techniques multifractales. Dans cette thèse nous avons montré que lorsqu'il existe une dépendance entre deux champs, celle ci est multi-échelle. L'utilisation du modèle multifractal universel (UM) a permis de quantifier le degré de cette dépendance. La qualité de l'estimation des paramètres UM dépend fortement de celle de l'invariance d'échelle observée: des séries temporelles présentant des tendances ne respectent pas cette invariance. Les effets de ces dernières sur l'estimation des paramètres UM peuvent être éliminés en utilisant la méthode de décomposition empirique modale dans l'espace physique. L'utilisation des données du champ de vitesse mesuré à l'aide de l'ADCP montre que, les pentes des spectres suivent un profil logarithmique selon la verticale, cela met en évidence que différents processus physiques opèrent le long de la colonne d'eau. Nous montrons également que l'hydrodynamique du lac est fortement perturbée à petite échelle au point du rejet d'eau pluviale. La dernière partie de la thèse examine ce que notre analyse à petites échelles apporte aux modèles numériques. Nous montrons que si les modèles déterministes arrivent à reproduire certains phénomènes à grande échelle, ils sont dans l'incapacité de représenter correctement les fluctuations à petites échelles, donc les processus physiques correspondants. L'analyse multifractale montre que la variabilité des champs physiques présente une forte intermittence. Le fait que la majorité des interactions biologiques/chimiques se produisent à petites échelles souligne la nécessité d'améliorer qualitativement les modèles de fermeture des équations de Navier-Stokes. Enfin, nous montrons que les fonctions de structures, observables statistiques de base en turbulence, ne permettent pas de caractériser de façon unique les champs non conservatifs et donc correspondent à des simulations multifractales non identiquesResearch in limnology has generally focused on natural lakes and dams. Moreover, the scientific challenges posed by urban lakes are numerous because of their large width and shallow depth resulting in complex problems that involve. This work is part of the project Petits Lacs Urbains Mesures Modèles Multi-Echelles (PLUMMME), founded by Région Île-de-France (DIM R2DS program). The project provides the high-resolution equipment measuring equipment used at Lake Créteil. Physical and biological measurements are the primary scope of this thesis, with some comparisons of measurements done between Lake Creteil and Lake Bourget. With this in mind, the first step of the thesis was to enhance currently available data. In order to do this we installed a station for the continuous measurement of: temperature, chlorophyll and light, also meteorological quantities such as wind speed, and air temperature were measured. The quantities were measured using two measuring chains comprising different sensors. Measurements were conducted in order to characterise hydrodynamics, using a current meter of type Acoustic Doppler Velocimeter (ADV) and a profiler of type Acoustic Doppler Current Profilers (ADCP) positioned at different points in the lake (centrally, and at the point of stormwater discharge). The analysis of the various measured fields shows that the lake is periodically stratified with a period of one week. We also identify the different modes of the internal waves that occur due to the effects of the wind. Spectral analysis was used to highlight the first scale invariant propriety of the different measured fields. Various physical processes (turbulence, stratification, near-wall flow) operating along the water column were also characterised using this method. The spectral analysis, however, does not provide information about the intermittency of the fluctuations of the measured fields, this can only be done using multifractal techniques. In this thesis, we have shown that when there is a dependence between two fields, the dependence is multiscale. The use of the Universal Multifractal (UM) model, allows one to quantify the degree of this dependence. The quality of the estimation of the UM parameters depends strongly on that of the observed scale: time-series with trends are not scaling. The effects of the latter on the estimation of UM parameters can be improved by the application of the Empirical Modal Decomposition method. The measured velocity data from the ADCP shows that the slope of the power spectra density follow a logarithmic profile along the depth of the lake, it shows that different physical processes operate along the water column. We also show that the hydrodynamics of the lake at small scale are strongly perturbed at the point of waterstorm discharge. The last part of the thesis is focused on what our analysis at small-scales brings to numerical models. We show that, if the deterministic models are able to reproduce some phenomena at large scale, they fail to describe the small-scale variability. the small scale variability and the physical processes involved. A multifractal analysis showed that the small-scale variability of the physical fields displays a strong intermittency, an extremely important feature for biological or chemical reactions and therefore for biological scenarios. Knowing that the majority of biological/chemical interactions occur at smaller scales, this result underlines the necessity to greatly improve the closure of the Navier-Stokes equations. Finally, we show that the structure function, a frequently used statistical tool in turbulence, do not uniquely characterize non-conservative fields, i.e., they do not correspond to identical simulations
39
Mish, Patrick F. "Mean Loading and Turbulence Scale Effects on the Surface Pressure Fluctuations Occurring on a NACA 0015 Airfoil Immersed in Grid Generated Turbulence." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/33751.
Abstract:
Detailed surface pressure measurements have been made on a NACA 0015 immersed in two grid generated homogenous flows at Re = 1.17 x 10^6 for a = 0°, 4°, 8°, 12°, 16°, and 20°. The goal of this measurement was to reveal and highlight mean loading and turbulence scale effects on surface pressure fluctuations resulting from turbulence/airfoil interaction. Also, measurements are compared with the theory of Amiet (1976a,b). The surface pressure response shows a dependance on angle of attack, the nature of which is related to the relative chord/turbulence scale. The dependance on turbulence scale appears to be non-monotonic at low reduced frequencies, wr = Pi*f*c/U with both an increase and decrease in unsteady pressure magnitude occuring with increasing mean load. A reduced frequency overlap region exists at wr > 10 where the two different scale flows begin to produce similar effects on the surface pressure with increasing angle of attack manifesting as a rise in unsteady surface pressure magnitude. Also, the interaction of the full 3-dimensional wavenumber spectrum affects the distance over which pressure fluctuations correlate and the extent of correlation is affected by angle of attack as demonstrated in the chordwise and spanwise pressure correlation. Amietâ s theory is shown to agree favorably with measurements in the leading edge region although demonstrates insufficiencies in predicting unsteady pressure phasing.Master of Science
40
Vollmer, David Russell. "Interaction of jet/front systems and mountain waves : implications for lower stratospheric aviation turbulence /." Raleigh, N.C. : Ft. Belvior, VA : Springfield, Va. : North Carolina State University ; Available to the public through the Defense Technical Information Center ; National Technical Information Service [distributor], 2008. http://www.dtic.mil/dtic/.
Abstract:
Thesis (Ph.D. in Philosophy (Marine, Earth, and Atmospheric Sciences))--North Carolina State University, July 2008.Title from reproduction cover. "July 2008." Thesis advisor(s): S. Pal Arya and Michael L. Kaplan. Performed by North Carolina State University; sponsored by the United States Air Force Institute of Technology, Wright-Patterson Air Force Base, Ohio. Includes vita. "A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Doctor of Philosophy, Marine, Earth, and Atmospheric Sciences from North Carolina State University. 2008."--P. [iv1]. "This research was funded by Air Force grant FA8718-04-C-0011."--p. ii. "Cl09-0007." Includes bibliographical references (p. 175-181). Also available online from the North Carolina State University Library and DTIC Online Web sites.
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Xiang, Xue. "Corner effects for oblique shock wave/turbulent boundary layer interactions in rectangular channels." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/287477.
Abstract:
In a rectangular cross-section wind tunnel a separated oblique shock reflection is set to interact with the turbulent boundary layer (oblique SBLI) both on the bottom wall and in the corner formed by the intersection of the floor with the side-walls. In such a scenario, shock-induced separation is often seen in each of the streamwise corners, resulting in a highly three-dimensional flow field in the near-wall region. To examine how the corner separations can affect the `quasi-two-dimensional' main interaction and by what mechanism this is achieved, an experimental investigation has been conducted. This examines how modifications to the corner separation influence an oblique shock reflection. The nature of the flow field is studied using flow visualisation, Pressure Sensitive Paint and Laser Doppler Anemometry. A nominal freestream Mach number of 2.5 is used for all experiments with a unit Reynolds number of $40\times10^6$m$^{-1}$, and the shock-generator angle is set to $8^\circ$. The flow conditions are chosen to result in substantial separations both in the corners and along the centreline for the baseline case, which is thought to be a good starting point for this study. The results show that the size and shape of central separation vary considerably when the onset and magnitude of corner separation change. The primary mechanism coupling these separated regions appears to be the generation of compression waves and expansion fans as a result of the displacement effect of the corner separation. The presence and strength of the expansion waves have been overlooked in previous studies. This is shown to modify the three-dimensional shock-structure and alter the adverse pressure gradient experienced by the tunnel floor boundary layer. It is suggested that a typical oblique SBLI in rectangular channels features several zones depending on the relative position of the corner waves and the main interaction domain. In particular, it has been shown that the position of the corner `shock' crossing point, found by approximating the corner compression waves by a straight line, is a critical factor determining the main separation size and shape. Thus, corner effects can substantially modify the central separation. This can cause significant growth or contraction of the separation length measured along the symmetry line from the nominally two-dimensional baseline value, giving a fivefold increase from the smallest to the largest observed value. Moreover, the shape and flow topology of the centreline separation bubble is also considerably changed by varying corner effects.
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Smith, Andrew Neilson. "The control of transonic shock wave/turbulent boundary layer interactions using streamwise slots." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620560.
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Ramsay, Stephen R. "The interaction of a 2D turbulent wake with a bluff body." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280712.
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Fomison, N. R. "The effects of bluntness and sweep on glancing shock wave turbulent boundary layer interaction." Thesis, Cranfield University, 1986. http://dspace.lib.cranfield.ac.uk/handle/1826/10550.
Abstract:
An
experimental investigation has been performed into the
effects
of leading edge bluntness and sweep on the mean flow
characteristics of a
glancing shock wave turbulent boundary layer
interaction. A series of blunt un swept shock generators (ranging
in
leading edge diameter from O to 1.0 ins) and a series of sharp
swept generators (covering angles of sweep from 0 to 75°) were
tested at incidences up to 30° at a Mach number of 2.4 and a
free stream Reynolds number of 2.6 x 106 m 1.
The results obtained, using a combination of oil flow
visualisation, static pressure measurements, schlieren photography
and
vapour screen visualisation, indicate that existing flow field
models can be extended to
include the more general configurations _
tested.
Leading edge diameter was found to be the major parameter
controlling the scale of the interaction produced by the blunted
models, with model incidence playing a secondary role, even at large
distances from the
generator. Existing methods for predicting the
scale of the
un swept sharp generator flow field are shown to provide
a reasonable estimate of the variation of upstream influence with
Reynolds number.
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Vieira, Rafael Fontes. "A numerical study on shock wave - boundary layer interaction flows." Instituto Tecnológico de Aeronáutica, 2013. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=2883.
Abstract:
This thesis addresses the important problem of shock wave--boundary layer interaction (SBLI) flows for aerospace engineering applications. Moreover, the work emphasizes the need for high fidelity simulations for the appropriate treatment of such flows. In this context, RANS solvers appear as a cost effective CFD approach. Therefore, the present work conducts studies in such a way to identify and to understand limitations, strengths and capabilities of RANS simulations for SBLI flows. Since turbulence modeling is an important issue on the accuracy of such simulations, the efforts here are concentrated on assessing the capabilities of several models that range from linear eddy-viscosity models (EVM) to Reynolds-stress closures (RSM). It would be expected that a RSM-type model could provide better solutions for a 3-D turbulent boundary layer under the action of high adverse pressure gradients, once such models allow for anisotropy between the Reynolds stress components. In order to achieve such goals, the configurations presented at the 2010 AIAA SBLI Workshop are chosen as the current test cases. Such test cases deal with high speed flows and very complex phenomena, including boundary layer separation. Meshes, composed of hexahedral and wedge elements, have been built. Mesh refinement and grid convergence studies are performed in order to identify a grid with a good compromise between accuracy and computational cost. In any event, even using the baseline grids, the present work has found that the computations are considerably expensive. Several simulations are presented for the test cases. Although no turbulence model has remarkably shown an outstanding performance over the others, the present work indicates that the SST and SA closures are the ones providing the best results for the test cases of interest here. Nonetheless, the two closures still present shortcomings in the simulation of SBLI flows. The overall simulation results using the RSM closure for the present SBLI test cases are not better than the SA and SST results. One must observe that the latter are much simpler turbulence models. Additional studies shall be focused on providing more robustness to the simulations with the 7-equation RSM turbulence model.
46
Barnhart, Paul Joseph. "Experimental investigation of unsteady shock wave turbulent boundary layer interactions about a blunt fin." Case Western Reserve University School of Graduate Studies / OhioLINK, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=case1058464929.
47
Sami, Kashmir. "Physics of three-dimensional normal shock wave/turbulent boundary layer interactions in rectangular channels." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610179.
48
Waindim, Mbu. "On Unsteadiness in 2-D and 3-D Shock Wave/Turbulent Boundary Layer Interactions." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1511734224701396.
49
Guenel, Mathieu. "Dissipation de marée dans les étoiles de faible masse et les planètes géantes : ondes inertielles, structure interne et rotation différentielle." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS307/document.
Abstract:
Cette thèse étudie les mécanismes de dissipation de marée dans les étoiles de faible masse, possédant comme notre Soleil une enveloppe convective externe (i.e. de types M à F), ainsi que dans les planètes géantes gazeuses similaires à Jupiter et Saturne. En particulier, nous cherchons à comprendre et à caractériser l’influence de la structure et de la dynamique internes de ces corps sur les différents mécanismes physiques à l’origine de cette dissipation afin d’évaluer leur importance relative.Dans le cas des planètes géantes, nous utilisons des modèles semi-analytiques préexistants et nous montrons que la dissipation induite par la présence éventuelle d’un cœur solide viscoélastique n’est pas négligeable par rapport à celle induite par les ondes inertielles (dont la force de rappel est l’accélération de Coriolis) dans l’enveloppe convective. Pour les étoiles de faible masse, nous développons de nouvelles méthodes semi-analytiques ainsi que des simulations numériques d’ondes inertielles de marée se propageant dans l’enveloppe convective externe, dont nous calculons et caractérisons la dissipation d’énergie associée. Pour la première fois, nous prenons en compte les effets d’une rotation différentielle latitudinale telle qu’observée dans le Soleil et prédite par de nombreuses simulations numériques de convection dans les étoiles de faible masse. Nous mettons en évidence l’existence de nouvelles familles de modes inertiels ainsi que l’importance des résonances de corotation pour la dissipation de marée. Enfin, nous dérivons une nouvelle prescription pour la viscosité turbulente appliquée à ces ondes de marées en prenant en compte l’influence de la rotation sur les propriétés de la convection le long de l’évolution des étoilesThis thesis studies the tidal dissipation mechanisms in low-mass stars that have an external convective envelope like the Sun (i.e. from M- to F-type stars), as well as in Jupiter- and Saturn-like gaseous giant planets. We particularly focus on understanding and characterizing the influence of the internal structure and dynamics of these bodies on the various physical mechanisms that cause this tidal dissipation, in order to assess their relative strength.In the case of giant planets, we use preexisting semi-analytical models and we show that the dissipation induced by the possible presence of a viscoelastic solid core is not negligible compared to the one induced by inertial waves (whose restoring force is the Coriolis acceleration) in the convective envelope. For low-mass stars, we perform a new semi-analytic study as well as numerical simulations of tidal inertial waves propagating in the external convective envelope, and we compute the associated energy dissipation. For the first time, the effects of a background latitudinal differential rotation, as observed in the Sun and predicted by various numerical simulations of convection in low-mass stars, is taken into account. We highlight the existence of new families of inertial modes as well as the importance of corotation resonances for tidal dissipation. Finally, we derive a new prescription for the turbulent viscosity applied to these tidal waves that takes into account the influence of rotation on the properties of convective flows along the evolution of stars
50
Adler, Michael C. "On the Advancement of Phenomenological and Mechanistic Descriptions of Unsteadiness in Shock-Wave/Turbulent-Boundary-Layer Interactions." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1553543774661509.