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1
Leung, Andrew Wing Che. "An investigation of three-dimensional shockwave/turbulent-boundary layer interaction." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284191.
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Galbraith, Daniel S. "Computational Fluid Dynamics Investigation into Shock Boundary Layer Interactions in the “Glass Inlet” Wind Tunnel." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1322053278.
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Bellinger, James. "Control of the oblique shockwave/boundary layer interaction in a supersonic inlet." Connect to resource, 2008. http://hdl.handle.net/1811/32065.
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Chokani, Ndaona. "A study of the passive effect on transonic shockwave/turbulent boundary layer interactions on porous surfaces." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293606.
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Bunnag, Shane. "Bleed Rate Model Based on Prandtl-Meyer Expansion for a Bleed Hole Normal to a Supersonic Freestream." University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1282330691.
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Grilli, Muzio [Verfasser], Nikolaus A. [Akademischer Betreuer] Adams, and Roberto [Akademischer Betreuer] Verzicco. "Analysis of the unsteady behavior in shockwave turbulent boundary layer interaction / Muzio Grilli. Gutachter: Roberto Verzicco ; Nikolaus A. Adams. Betreuer: Nikolaus A. Adams." München : Universitätsbibliothek der TU München, 2013. http://d-nb.info/1046404741/34.
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Boyer, Nathan Robert. "The Effects of Viscosity and Three-Dimensionality on Shockwave-Induced Panel Flutter." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu156616766854713.
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Philit, Mickaël. "Modélisation, simulation et analyse des instationnarités en écoulement transsonique décollé en vue d'application à l'aéroélasticité des turbomachines." Thesis, Ecully, Ecole centrale de Lyon, 2013. http://www.theses.fr/2013ECDL0033/document.
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Dans la conception des turbomachines modernes, la prédiction des phénomènes aéroélastiques est devenue un point clé. La tendance à réduire la masse et à augmenter la charge des composants aérodynamiques accroit le risque de rupture. Dans un tel contexte, la compréhension et la bonne prédiction des diverses instabilités constituent un enjeu industriel et scientifique majeur. Le présent travail de recherche a pour objectif d’améliorer la prédiction des phénomènes instationnaires intervenant dans les problèmes d’aéroélasticité en turbomachines. Cette thèse est plus particulièrement axée sur la simulation de l’interaction onde de choc/couche limite. Le support d’étude est une tuyère transsonique présentant un écoulement avec des zones décollées. L’oscillation forcée de l’onde de choc est simulée grâce à une méthode de petites perturbations instationnaires couplée avec une hypothèse de turbulence variable. Cette approche est validée par comparaison avec des mesures. Elle permet une prédiction tout à fait satisfaisante du premier harmonique de pression sur la paroi de la tuyère. Ce travail a montré la nécessité de linéariser le modèle de turbulence. Le besoin de dériver le modèle de turbulence nous a amené à investiguer la modélisation faite pour prédire l’interaction onde de choc/couche limite. Un modèle de turbulence à deux équations complété par une équation de « retard » est implémenté afin de capter un déséquilibre de la turbulence. Les résultats obtenus en tuyère sont cohérents avec la théorie mais une surproduction d’énergie turbulente en présence de bord d’attaque rend le modèle inefficace pour des configurations de turbomachines. Au final, l’introduction d’un limiteur de viscosité turbulente dans un modèle de turbulence à deux équations s’avère donner de bons résultats. La méthode de dérivation du modèle est alors présentée sur le modèle de Wilcox proposé en 2008. Enfin, la technique de linéarisation est étendue à la problématique aéroélastique. Une approche de couplage fluide-structure faible est adoptée. L’oscillation structurelle des aubages suivant les modes propres est considérée mais en laissant la fréquence évoluer au cours du couplage. La nouvelle méthode utilisée s’appuie sur la construction d’un méta-modèle du comportement dynamique du fluide afin de résoudre directement le système fluide-structure couplé. Cette technique est validée sur une configuration de grille annulaire de turbine en haut subsonique et présente l’avantage d’un temps de calcul réduitIn modern turbomachinery design, predicting aerolastic phenomena has become a key point. The development of highly loaded components, while reducing their weight, increases the risk of failure. In this context, good understanding and prediction of various instabilities are a major industrial and scientific challenge. This research work aims to improve the prediction of unsteady phenomena involved in turbomachinery aeroelasticity. This study focuses especially on the simulation of shock wave/boundary layer interaction. To begin with, a transonic nozzle separated flow is investigated. Forced oscillation of the shock wave system is simulated through a small unsteady perturbation method combined with the assumption of variable turbulence. This approach is validated against exprimental measurements. The first harmonic of pressure on the wall of the nozzle is predicted quite satisfactorily. The need to linearize the turbulence model was shown of high importance. Deriving the turbulence model, leads us to investigate the turbulence modeling performed to predict the shockwave/boundary layer interaction. A two equations turbulence model supplemented by a "time-lagged" equation is implemented to capture non-equilibrium effects of turbulence. All achieved results for a nozzle are consistent with theory, but overproduction of turbulent kinetic energy at leading edge makes the model useless for turbomachinery configurations. However, the introduction of an eddy viscosity stress limiter inside a two-equation turbulence model proves to give good results. The derivation method is thus presented on such a model, precisely on Wilcox model proposed in 2008. Finally, the linearization technique is extended to aeroelastic problems. A loose fluid-structure coupling strategy is adopted. The structural oscillation of the blades is considered for eigen-modes but frequency is free to change during coupling resolution. The new approach is based on the building of a meta-model to describe the fluid dynamic behavior in order to solve directly the coupled fluid-structure system. This technique is validated on a standard high subsonic turbine configuration and takes advantage of a reduced computation time
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Frank, Donya P. "Wave-Current Bottom Boundary Layer Interactions." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1229087949.
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Touber, Emile. "Unsteadiness in shock-wave/boundary layer interactions." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/161073/.
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The need for better understanding of the low-frequency unsteadiness observed in shock wave/turbulent boundary layer interactions has been driving research in this area for several decades. This work investigates the interaction between an impinging oblique shock and a supersonic turbulent boundary layer via large-eddy simulations. Special care is taken at the inlet in order to avoid introducing artificial low-frequency modes that could affect the interaction. All simulations cover extensive integration times to allow for a spectral analysis at the low frequencies of interest. The simulations bring clear evidence of the existence of broadband and energetically-significant low-frequency oscillations in the vicinity of the reflected shock, thus confirming earlier experimental findings. Furthermore, these oscillations are found to persist even if the upstream boundary layer is deprived of long coherent structures. Starting from an exact form of the momentum integral equation and guided by data from large-eddy simulations, a stochastic ordinary differential equation for the reflectedshock foot low-frequency motions is derived. This model is applied to a wide range of input parameters. It is found that while the mean boundary-layer properties are important in controlling the interaction size, they do not contribute significantly to the dynamics. Moreover, the frequency of the most energetic fluctuations is shown to be a robust feature, in agreement with earlier experimental observations. Under some assumptions, the coupling between the shock and the boundary layer is mathematically equivalent to a first-order low-pass filter. Therefore, it is argued that the observed lowfrequency unsteadiness is not necessarily a property of the forcing, either from upstream or downstream of the shock, but simply an intrinsic property of the coupled dynamical system.
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Bhide, Kalyani R. "Shock Boundary Layer Interactions - A Multiphysics Approach." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1543994392025663.
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Findell, Kirsten L. (Kirsten Lynn). "Atmospheric controls on soil moisture-boundary layer interactions." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/44509.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2001.Includes bibliographical references (leaves 163-168).
This thesis addresses the question of how the early morning atmospheric thermodynamic structure affects the interaction between the soil moisture state and the growth and development of the boundary layer (BL), leading to the triggering of convection. It is concluded that in mid-latitudes, for matters of convective triggering and response to land surface conditions, the critical portion of the atmospher~approximately1 to 3 km above the ground surface is independent of geographic location and local synoptic setting. As long as the low levels of the troposphere are relatively humid but not extremely close to saturation, a negative feedback between soil moisture and rainfall is likely when the early morning temperature lapse rate in this region is dry adiabatic; a positive feedback is likely when it is moist adiabatic; and when there is a temperature inversion in this region, deep convection cannot occur, independent of the soil moisture. Additionally, when the low levels of the troposphere are extremely dry or very close to saturation, the occurrence of convection is determined solely by the atmospheric conditions. Essential characteristics of the temperature structure of the early-morning atmosphere are captured by a new thermodynamic measure, the Convective Triggering Potential (CTP), developed to distinguish between soundings favoring rainfall over dry soils from those favoring rainfall over wet soils. Many measures of atmospheric humidity are effective at separating atmospherically-controlled cases from cases where the land surface conditions can influence the likelihood for convection, but Hi low, a variation of a humidity index, proved most effective. A one-dimensional model of the planetary boundary layer (BL) and surface energy budget has been modified to allow the growing BL to entrain air from an observed atmospheric sounding. The model is used to analyze the impact of soil saturation on BL development and the triggering of convection in different atmospheric settings. Results from this 1D model and from the three-dimensional Fifth-Generation Penn State/NCAR Mesoscale Model (MM5) show a small but significant positive soil moisture-rainfall feedback in Illinois. This is consistent with an analysis of the distribution of early morning sounding values of CTP and Hi low from Illinois, though wind effects important in the MM5 simulations are not captured by the CTP-HIhow framework. From the MM5 simulations, it is concluded that the land surface condition can impact the potential for convection only when the atmosphere is not already predisposed to convect or not to convect. This atmospheric predisposition can be determined by analyzing the CTP, the Hi low, and the vertical profile of the winds. Analyses of Hi low scatter plots from radiosonde stations across the contiguous 48 United States reveal that positive feedbacks are likely in much of the eastern half of the country. The only area showing a potential negative feedback is in the Dryline and Monsoon Region of the arid southwest. Land surface conditions are unlikely to impact convective triggering in the rest of the western half of the country. Use of the lD BL model at four additional stations confirms that HilowTP-Hi low framework used in this nationwide analysis is valid for regions far removed from Illinois, where it was originally developed.
by Kirsten Lynn Findell.
Ph.D.
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Al-Salman, Adam. "Nonlinear modal interactions in a compressible boundary layer." Thesis, Imperial College London, 2003. http://hdl.handle.net/10044/1/61537.
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It is well known that boundary layers in the supersonic regime can support multiple instability modes, including the well-documented first and second modes. The main aim of this thesis is to investigate nonlinear modal interactions. Since an instability mode attains its maximum magnitude in its critical layer (i.e. the region surrounding the position where the basic flow velocity is equal to the phase velocity), particularly effective interactions can take place among modes which share the same critical layer. As a first step, we solved the compressible Rayleigh equation, using parameters representing practical supersonic flows. Our calculations show that the resonant triad and phase-locked interactions can occur among purely first modes, or a certain combination of first and second modes. A new type of interaction between two or more modes which are frequency-locked, was identified. Each of these interactions has been studied in the so-called nonlinear nonequilibrium viscous critical-layer regime. For the resonant triad interaction, we derived a system of integro-partial-differential equations, which govern the spatial-temporal modulation of a triad, consisting of two oblique and one planar wavetrains. In the first stage, the amplitude of the planar wavetrain is governed by a linear equation. The oblique wavetrain amplitudes are governed by a set of coupled nonlinear equations, due to the quadratic interaction between the oblique and the planar wavetrains, which takes place in their common critical layers. These equations are solved for the two cases of interest where each wavetrain has a discrete spectrum or a narrow band continuous spectrum. Our results are able to capture experimental observations qualitatively. The disturbance enters the second stage once the planar wave has grown to such an extent that its self nonlinearity becomes significant. We find that the viscosity law can affect the form of the nonlinear term in the planar wave amplitude equation. As a result of this, the solution to this equation saturates. The previously super-exponential growth of the oblique wave is reduced to exponential growth. Similarly for the phase-locked interaction, we derived a system of integro-partial-differential equations, which govern the spatial-temporal modulation of a pair of wavetrains. Again in the first stage of the development, the planar mode is governed by a linear equation, but it interacts with the obhque mode to generate a large difference mode, which in turn interacts with the planar mode, to contribute a cubic nonlinear term to the amplitude equation of the oblique mode. These equations are solved for the case of interest where the wavetrains have a narrow band continuous spectra. The evolution of these waves in the second stage where the planar wave becomes nonlinear is also investigated. Next we studied the interaction between two oblique modes which are frequency-locked, in the sense that they all have the same streamwise wave number and frequency. This is a unique feature of supersonic flows, and may be relevant for the K-type of transition. We also investigate this type of interaction between two pairs of oblique modes. Finally we considered the streamwise-spanwise modulation of a nearly planar acoustic mode in a hypersonic boundary layer. We derived an evolution system consisting of an amplitude equation coupled to the two strongly nonlinear equations for the vorticity and temperature in the critical layer.
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Atkin, Christopher John. "A numerical study of unsteady shock/boundary layer interactions." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358375.
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Yeung, Archie Fu-Kuen. "The passive control of swept-shock/boundary-layer interactions." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388505.
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Lawal, Abdulmalik Adinoyi. "Direct numerical simulation of transonic shock/boundary-layer interactions." Thesis, University of Southampton, 2002. https://eprints.soton.ac.uk/47089/.
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Gibson, Thomas Mark. "The passive control of shock-wave/boundary-layer interactions." Thesis, University of Cambridge, 1997. https://www.repository.cam.ac.uk/handle/1810/272691.
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Giannakopoulou, Evangelia Maria. "Land-boundary layer-sea interactions in the Middle East." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/10479.
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Understanding the land–boundary layer–sea interactions is a primary target both in the context of low-level jet (LLJ) development and landscape alterations. This thesis attempts to address and study these interactions in the Middle East. The thesis investigates the summertime LLJ over the Persian Gulf, known as the Shamal. Terrain height, land-sea and novel mountain slope sensitivity experiments were conducted and compared with a control run. It was found that the Weather Research and Forecasting (WRF) model accurately simulates the LLJ’s vertical structure, nocturnal features and strong diurnal oscillation of the wind, and that orography, mountain slope and land/sea breezes determine the Shamal diurnal variation of wind speed and wind direction. The Iranian mountain range not only channels the northwesterly winds but also provides a barrier for the easterly monsoon airflow. The steep slopes cause increased wind speeds; however, the shallow slopes reveal a stronger diurnally varying wind direction due to larger diurnal heating of the sloping terrain. The land breeze and the lower friction over the sea increase the intensity of the nocturnal jet over the Gulf. To determine the effects of the Nile Delta man-induced greening on local climate, the WRF model was used to compare control simulations, which employ the present-day Nile Delta landscape, with desertification experiments in which the Nile Delta is replaced by desert. It was found that the low surface albedo of the present-day agricultural Nile Delta increases net radiation, which in turn raises potential evapotranspiration (PET). This suggests that agricultural use increases the water demand by enhancing PET. Non-local effects were also examined. It was found that a frontal system over the eastern Mediterranean Sea, associated with a storm event, is shifted farther away from the coast. This shift is attributed to a stronger land breeze in the present-day land-cover.
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Grossman, Ilan Jesse. "Effect of confinement on shock wave-boundary layer interactions." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/47924.
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Shock wave-boundary layer interactions (SWBLIs) are an inevitable feature of compressible flow and can have a large detrimental effect on the performance of aerodynamic applications. To address and design to accommodate them, requires detailed understanding of the underlying flow mechanisms. At present, our knowledge of these mechanisms is insufficient to accurately predict SWBLI behavior. This experimental study attempts to provide a better understanding of some of these mechanisms by focusing on the three- dimensionality inherent in oblique SWBLIs. The test configuration consists of an oblique shock wave in Mach 2 flow in a rectangular test section at flow deflection angles of 8° , 10° , and 12°. The key parameters of test section effective aspect ratio (AReff) and shock generator geometry are varied to assess their ability to amplify/attenuate the three-dimensionality of a nominally two-dimensional SWBLI. An innovative traversable shock generator with interchangeable wedge geometries allow the effects of AReff , expansion fan placement, and side-wall gap to be studied. The flow is investigated by employing Schlieren photography, surface flow visualization, static pressure measurements, Laser Doppler Anemometry and Particle Image Velocimetry. It is observed that with an increase in AReff, or a downstream movement of the expansion fan, or a decrease in side-wall gap, the SWBLI and shock-induced separation will grow. The growth of the separated region exhibits an increase in three-dimensionality and at high AReff the regular reflection is observed to evolve into a Mach reflection without an increase in incident shock strength. Models are proposed to explain the observed behavior as a function of separation growth and a reduction of the influence of free interaction theory.
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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.
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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
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Bruce, P. J. K. "Transonic shock/boundary layer interactions subject to downstream pressure perturbations." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597030.
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In the present study, an experimental investigation into the response of transonic SBLIs to periodic downstream pressure perturbations in a parallel walled duct has been conducted. Tests have been carried out for shock strengths of M∞ = 1.4 and 1.5 with pressure perturbation frequencies in the range 16-90 Hz. Analysis of the steady interaction at M∞ = 1.3, 1.4 and 1.5 has also been made. For all unsteady test cases, the transonic shock was observed to undergo periodic oscillatory motion in the streamwise direction. This motion changes the relative shock strength, which causes the inter-action structure to vary during oscillations. The dynamics of shock motion are determined primarily by the imposed pressure ratio. At high frequency, viscous effects were observed to have an effect on the interaction structure and shock dynamics. Inviscid analytical and computational models for the prediction of shock dynamics in ducts have been developed. Based on these, a non-dimensional model for the relationship between the amplitude and frequency of shock motion in a diverging duct has been proposed. At low frequencies, shock oscillation amplitude is constant and dominated by duct geometry. At moderate frequencies, amplitude is inversely proportional to frequency and duct geometry is unimportant. At high frequencies, the amplitude of oscillations are small and viscous effects become significant. These viscous effects are most significant during rapid changes in relative shock strength. Shock acceleration, which increases with frequency, is the key variable which determines their importance. It is postulated that the finite time taken for changes in the viscous SBLI structure to occur is at the origin of the observed behaviour. The relevance of the study to real-world applications where unsteady SBLIs occur is discussed.
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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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Bowles, Robert Ian. "Applications of nonlinear viscous-inviscid interactions in liquid layer flows and transonic boundary layer transition." Thesis, University College London (University of London), 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.489006.
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Paunova, Irena T. "Explicit numerical study of aerosol-cloud interactions in boundary layer clouds." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100670.
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Aerosol-cloud interactions, the mechanisms by which aerosols impact clouds and precipitation and clouds impact aerosols as they are released upon droplet evaporation, are investigated by means of explicit high-resolution (3 km) numerical simulations with the Mesoscale Compressible Community (MC2) model. This model, which is non-hydrostatic and compressible, was extended by including separate continuity equations for dry and activated multi-modal aerosol, and for chemical species. The sources and sinks include: particle activation, solute transfer between drops, generation of extra soluble material in clouds via oxidation of dissolved SO2, and particle regeneration. The cloud processes are represented by an advanced double-moment bulk microphysical parameterization.Three summertime cases have been evaluated: a marine stratus and a cold frontal system over the Bay of Fundy near Nova Scotia, formed on 1 Sep 1995 and extensively sampled as a part of the Radiation, Aerosol, and Cloud Experiment (RACE); and a continental stratocumulus, formed over the southern coast of Lake Erie on 11 July 2001. The marine stratus and the frontal system have been examined for the effects of aerosol on cloud properties and thoroughly evaluated against the available observations. The frontal system and the continental stratocumulus have been evaluated for the effects of cloud processing on the aerosol spectrum.
The marine stratus simulations suggest a significant impact of the aerosol on cloud properties. A simulation with mechanistic activation and a uni-modal aerosol showed the best agreement with observations in regards to cloud-base and cloud-top height, droplet concentration, and liquid water content. A simulation with a simple activation parameterization failed to simulate essential bulk cloud properties: droplet concentration was significantly underpredicted and the vertical structure of the cloud was inconsistent with the observations. A simulation with a mechanistic parameterization and a bi-modal aerosol, including a coarse mode observed in particle spectra below cloud, showed high sensitivity of droplet concentration to the inclusion of the coarse mode. There was a significant reduction in droplet number relative to the simulation without the coarse mode. A similar change occurred in the precipitating system preceding the stratus formation, resulting in an enhancement of precipitation in the weaker (upstream) part of the system while the precipitation in the more vigorous (downstream) part of the system remained almost unaffected.
Aerosol processing via collision-coalescence and aqueous chemistry in the non-drizzling stratocumulus case suggests that impact of the two mechanisms is of similar magnitude and can be as large as a 3-5 % increase in particle mean radius. A more detailed analysis reveals that the impact of chemical processing is oxidant-limited; beyond times when the oxidant (H 2O2) is depleted (∼ 40 minutes), the extent of processing is determined by supply of fresh oxidant from large-scale advection (fresh gaseous emissions are not considered). Aerosol processing via drop collision-coalescence alone suggests, as expected, sensitivity to the strength of the collection process in clouds. Larger particle growth, up to 5-10 %, is observed in the case of the frontal clouds, which exhibit stronger drop collection compared to that in the stratocumulus case. The processed aerosol exerted a measurable impact on droplet concentrations and precipitation production in the frontal clouds. For the case modeled here, contrary to expectations, the processed spectrum (via physical processing) produced higher droplet concentration than the unprocessed spectrum. The reasons explaining this phenomenon and the resulting impact on precipitation production are discussed.
The current work illustrates the complexity of the coupled system at the cloud system scales, revealed earlier at much smaller large eddy scales. If future parameterizations of the regional effect of aerosols on clouds are to be developed, careful consideration is required of the many of feedbacks in the boundary layer.
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Coschignano, Andrea. "Normal shock wave-boundary layer interactions in transonic intakes at incidence." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/278058.
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During take-off, the aerodynamic performance of a transonic engine intake is dominated by the flow-field over the nacelle lower lip, around which the flow might accelerate to supersonic speeds. A shock wave might appear and impinge on the incoming boundary layer. Flow separation may result from this interaction, leading to severe flow distortion. In order to maximise fuel efficiency by reducing aerodynamic drag, slimmer nacelle designs are currently being pursued by manufacturers. Understanding the impact of design choices on the development of shock-wave boundary layer interactions (SBLI) is crucial, as these phenomena have a severe effect on the stability of the flow inside the nacelle. The available literature is rather scarce and unable to assess the nature and severity of SBLIs, which remain to be addressed in the context of nacelles at incidence. To address this shortcoming, a novel experimental rig has been designed exclusively to assess the detrimental effects resulting from shock-induced separation for a number of intake lip shapes and inflow conditions. For the reference intake shape, the flow field around the lower lip during on-design take-off conditions was found to be relatively benign, with minimal shock-induced separation. As incidence is increased by 2◦, from the reference incidence of 23◦, this separation gets noticeably larger and unsteadiness develops. The downstream boundary layer is more distorted and reflects the losses across the interaction. This is exacerbated at even higher incidence. Increasing the mass flow rate over the lip up to 15% of the initial value had only minor effects on performance. The parametric investigation revealed a significant effect of lip shape on the position and severity of the SBLI. In particular, a slimmer nacelle performed poorly, favouring shock development very close to the lip nose and promoting large scale separation as the incidence increases. From correlation studies based on the parametric investigation, it appears that the extent of shock-induced separation is the main factor affecting the aerodynamic performance. Somewhat surprisingly, this was found to be independent of shock strength but potentially related to the severity of the diffusion downstream of the shock. Alongside delaying flow reattachment, this diffusion is also likely to have a direct detrimental effect on the boundary layer development close to the engine fan.
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Bura, Romie Oktovianus. "Laminar/transitional shock-wave/boundary-layer interactions (SWBLIs) in hypersonic flows." Thesis, University of Southampton, 2004. https://eprints.soton.ac.uk/47605/.
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Numerical investigations of laminar shock-wave/boundary-layer interactions (SWBLIs) in hypersonic flow have been carried out at M∞ = 6.85 and M∞ ≈ 8, with unit Reynolds numbers ranging from 2.0 x 106 m- l to 7.60 x 106 m- l. This thesis deals with a simplified 2-D geometric configuration to simulate SWBLIs on vehicle surfaces or engine intakes, i.e. the interaction of an oblique shock (produced by a wedge) impinging on an incoming laminar boundary-layer on an isothermal flat plate. The numerical simulations were performed with weak/moderate to strong shock. The results were compared with available theoretical and experimental results. Limited experimental work at M∞ = 6.85 for obtaining qualitative data were performed to provide the location of separation and re-attachment points using surface oil flow. Schlieren photographs were taken to provide the general flow features. A comprehensive analysis was performed on the 2-D numerical results with various Mach numbers, Reynolds numbers and shock strengths, to verify whether numerical solutions were able to confirm the established trends for the laminar free-interaction concept. An analysis was also performed using a well-established power-law relationship of pressure and heat flux in the region of interactions. An unstable first oblique mode disturbance was imposed with the strongest wedge angle, 9°, at M∞ = 6.85 and unit Reynolds number 2.45 x 106 m- l to determine the boundary-layer stability and its propensity to undergo transition in the linear regime. Several unsteady 3-D simulations were performed with varied parameters. Streamwise vortices were generated in all cases especially downstream of maximum separation bubble height. However, as the amplifications of the disturbance were quite small, transition was found to be unlikely at these conditions
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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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Schreiber, Olivier. "Aerodynamic interactions between bodies in relative motion." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/11693.
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Bhanderi, Harish Shantilal. "Lag-entrainment method in the case of transonic shock/boundary layer interactions." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614132.
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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/.
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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).
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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.
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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.
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Huang, Hsin-Yuan. "Investigation of land surface-convective boundary layer interactions using large-eddy simulation." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1835573641&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Cash, Allison Nicole. "Computational studies of fully submerged bodies, propulsors, and body/propulsor interactions." Master's thesis, Mississippi State : Mississippi State University, 2001. http://library.msstate.edu/etd/show.asp?etd=etd-11082001-113555.
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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.
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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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Good, Emily Irene. "Organic-mineral interactions across the benthic boundary layer in the northeast Atlantic Ocean." Thesis, University of Edinburgh, 2002. http://hdl.handle.net/1842/13931.
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Bulk elemental and biochemical yields in samples collected across the benthic boundary layer (BBL) in the Northeast Atlantic indicated the BBL to be a key site of organic matter (OM) alteration and played a pivotal role in determining the organic carbon: surface area ratio (OC: SA) ratio of material deposited in the sediments in this region. Evidence for the seasonal nature of OM inputs to the BBL in the Northeast Atlantic was found in two of the three investigated sites. The seasonal deposition of material associated with the spring bloom led to the presence of a substantial layer of phytodetritus material at one site. Although this material was not rich in OC, it contained elevated yields of labile biochemicals that suggested the potential importance of such material to deep-sea benthic nutrition. The majority of OM within the sediments in the deep Northeast Atlantic appeared to be sorbed to mineral grains displaying SA-normalised OC loadings below those typically observed on continental margins (i.e. <0.5 mg QC m-2) indicating that OM remineralisation processes are extremely efficient in this region. An investigation into the possible influences on OC preservation and burial in the Northeast Atlantic and in other diverse continental margin sediments, suggested that only the length of time that sedimentary OM was exposed to oxic porewaters displayed a consistent relationship with sediment OC: SA ratios and OC burial efficiencies. Sediment oxygen exposure time, therefore, appear to be a primary control on OM burial.
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Sotiropoulou, Georgia. "The Arctic Atmosphere : Interactions between clouds, boundary-layer turbulence and large-scale circulation." Doctoral thesis, Stockholms universitet, Meteorologiska institutionen (MISU), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-134525.
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Arctic climate is changing fast, but weather forecast and climate models have serious deficiencies in representing the Arctic atmosphere, because of the special conditions that occur in this region. The cold ice surface and the advection of warm air aloft from the south result in a semi-continuous presence of a temperature inversion, known as the “Arctic inversion”, which is governed by interacting large-scale and local processes, such as surface fluxes and cloud formation. In this thesis these poorly understood interactions are investigated using observations from field campaigns on the Swedish icebreaker Oden: The Arctic Summer Cloud Ocean Study (ASCOS) in 2008 and the Arctic Clouds in Summer Experiment (ACSE) in 2014. Two numerical models are also used to explore these data: the IFS global weather forecast model from the European Center for Medium-range Weather Forecasts and the MIMICA LES from Stockholm University. Arctic clouds can persist for a long time, days to weeks, and are usually mixed-phase; a difficult to model mixture of super-cooled cloud droplets and ice crystals. Their persistence has been attributed to several mechanisms, such as large-scale advection, surface evaporation and microphysical processes. ASCOS observations indicate that these clouds are most frequently decoupled from the surface; hence, surface evaporation plays a minor role. The determining factor for cloud-surface decoupling is the altitude of the clouds. Turbulent mixing is generated in the cloud layer, forced by cloud-top radiative cooling, but with a high cloud this cannot penetrate down to the surface mixed layer, which is forced primarily by mechanical turbulence. A special category of clouds is also found: optically thin liquid-only clouds with stable stratification, hence insignificant in-cloud mixing, which occur in low-aerosol conditions. IFS model fails to reproduce the cloud-surface decoupling observed during ASCOS. A new prognostic cloud physics scheme in IFS improves simulation of mixed-phase clouds, but does not improve the warm bias in the model, mostly because IFS fails to disperse low surface-warming clouds when observations indicate cloud-free conditions. With increasing summer open-water areas in a warming Arctic, there is a growing interest in processes related to the ice marginal zones and the summer-to-autumn seasonal transition. ACSE included measurements over both open-water and sea-ice surfaces, during melt and early freeze. The seasonal transition was abrupt, not gradual as would have been expected if it was primarily driven by the gradual changes in net solar radiation. After the transition, the ocean surface remained warmer than the atmosphere, enhancing surface cooling and facilitating sea-ice formation. Observations in melt season showed distinct differences in atmospheric structure between the two surface types; during freeze-up these largely disappear. In summer, large-scale advection of warm and moist air over melting sea ice had large impacts on atmospheric stability and the surface. This is explored with an LES; results indicate that while vertical structure of the lowest atmosphere is primarily sensitive to heat advection, cloud formation, which is of great importance to the surface energy budget, is primarily sensitive to moisture advection.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.
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Sansica, Andrea. "Stability and unsteadiness of transitional shock-wave/boundary-layer interactions in supersonic flows." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/385891/.
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The aim of this research is to study the effect of transition location on the interaction between an oblique shock-wave and a boundary-layer. A large set of direct and large eddy simulations are performed with an in-house high-order fully-parallelised finite difference compressible Navier-Stokes solver to study the inherent instability and unsteady behaviour of laminar, transitional and turbulent interactions. The numerical simulations are compared with the experiments conducted at the Novosibirsk State University as part of the EU-FP7 TFAST project, providing a better understanding of the fundamental mechanisms of the shock-wave/boundary-layer interaction (SWBLI). As well as the characteristics of the interactions, interest is also focused on methods to control the transition location. Three distinct forcing techniques are used to obtain different transition scenarios for a laminar SWBLI at free-stream Mach number of 1.5. An oblique mode breakdown caused by forcing the most unstable eigenmodes, predicted by the local linear stability theory, is compared with a bypass-like transition due to high-amplitude free-stream acoustic disturbances. A non-thermal plasma flow actuation device is also used, however showing a low applicability to supersonic flows due to the high electric power required to trigger transition. Attention is also focused on the response of a laminar shock-induced separation bubble. For both 2D and 3D configurations, a low-frequency response is found for the first time in a laminar SWBLI, even when the separation bubble is only forced internally, therefore supporting the idea that the separated region is influenced by internal mechanisms. The SWBLI is further analysed via linear and nonlinear stability approaches, including local stability theory or parabolised stability equations based tools. The response of the separated region for increasing shock intensities is studied and the stability based tools provide satisfactory results even for largely separated boundary-layers.
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Saad, Mohd Rashdan. "Experimental studies on shock boundary layer interactions using micro-ramps at Mach 5." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/experimental-studies-on-shock-boundary-layer-interactions-using-microramps-at-mach-5(71f1e11c-dbfd-443a-a9ee-e3fc160176f1).html.
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Shock boundary layer interactions (SBLI) is an undesirable event occurring in high-speed air-breathing propulsion system that stimulates boundary layer separation due to adverse pressure gradients and consequently lead to ow distortion and pressure loss in the intake section. Therefore it is essential to apply ow control mechanisms to prevent this phenomenon. This study involves a novel ow control device called micro-ramp, which is a part of the micro-vortex generator family that has shown great potential in solving the adverse phenomenon. The term micro refers to the height of the device, which is smaller than the boundary layer thickness, δ. It is important to highlight the two main novelties of this investigation. Firstly, it is the first micro-ramp study conducted in the hypersonic ow regime (Mach 5) since most of the previous micro-ramp studies were only performed in subsonic, transonic and supersonic flows. Another novelty is the various experimental techniques that were used in single study for example schlieren photography, oil-dot and oil- ow visualisation and conventional pressure transducers. In addition, advanced ow diagnostic tools such as infrared thermography, pressure sensitive paints (PSP) and particle image velocimetry (PIV) were also employed. T
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Threadgill, James. "Unsteadiness of shock wave boundary layer interactions across multiple interaction configurations and strengths." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/48475.
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Shock Wave Boundary Layer Interactions (SWBLIs) represent complex flow phenomena that remain poorly understood despite their prevalence on high-speed vehicles, in part due to their complicated underlying physics. In particular, the mechanisms that drive the high-amplitude, low-frequency unsteadiness within the interaction have perplexed researchers for many years while remaining a limitation to vehicle performance and a potential danger to airframe integrity. This investigation has specifically examined the influence of interaction strength and configuration type on the characteristic unsteady behaviour that describes the flow environment. Until now, researchers have typically focused on testing a specific configuration in a given test facility. This approach can obscure meaningful conclusions that may be drawn due to the interference of the test environment. The present research effort therefore tackles this flaw by assessing flow behaviours across a range of SWBLIs, all tested within a common environment. Four strengths of oblique shock reflection interactions and two strengths of compression ramp interactions have been assessed and compared. Experiments have been conducted in the Imperial College Supersonic Wind Tunnel with a Mach 2 turbulent incoming boundary layer with momentum thickness Reynolds number of 8000. Using a combined approach of synchronised PIV and fast-response wall-pressure measurements the unsteady elements to the interactions have been investigated. The spectral evolutions of unsteady wall-pressure disturbances are assessed throughout each of the interactions. Results confirm that the high-frequency component of the separation shock spectral content is common across all interactions. Meanwhile, low-frequency amplitudes scale with the interaction length, acting to decrease the characteristic frequency used to describe such motion when the interaction strength is increased. Instantaneous shock structures have also been identified which confirm the presence of two unsteady mechanisms governing the dynamics of the separation shock: rotation and translation. Quasi-steady modelling of these mechanisms indicates how their relative dominance varies with interaction strength and configuration type. This body of work represents a unique assessment of valuable data that is crucial to the development of unsteady SWBLI understanding.
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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.
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Wang, Zhen, and Zhen Wang. "Interactions Between Atmospheric Aerosols and Marine Boundary Layer Clouds on Regional and Global Scales." Diss., The University of Arizona, 2018. http://hdl.handle.net/10150/626640.
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Airborne aerosols are crucial atmospheric constituents that are involved in global climate change and human life qualities. Understanding the nature and magnitude of aerosol-cloud-precipitation interactions is critical in model predictions for atmospheric radiation budget and the water cycle. The interactions depend on a variety of factors including aerosol physicochemical complexity, cloud types, meteorological and thermodynamic regimes and data processing techniques. This PhD work is an effort to quantify the relationships among aerosol, clouds, and precipitation on both global and regional scales by using satellite retrievals and aircraft measurements. The first study examines spatial distributions of conversion rate of cloud water to rainwater in warm maritime clouds over the globe by using NASA A-Train satellite data. This study compares the time scale of the onset of precipitation with different aerosol categories defined by values of aerosol optical depth, fine mode fraction, and Ångstrom Exponent. The results indicate that conversion time scales are actually quite sensitive to lower tropospheric static stability (LTSS) and cloud liquid water path (LWP), in addition to aerosol type. Analysis shows that tropical Pacific Ocean is dominated by the highest average conversion rate while subtropical warm cloud regions (far northeastern Pacific Ocean, far southeastern Pacific Ocean, Western Africa coastal area) exhibit the opposite result. Conversion times are mostly shorter for lower LTSS regimes. When LTSS condition is fixed, higher conversion rates coincide with higher LWP and lower aerosol index categories. After a general global view of physical property quantifications, the rest of the presented PhD studies is focused on regional airborne observations, especially bulk cloud water chemistry and aerosol aqueous-phase reactions during the summertime off the California coast. Local air mass origins are categorized into three distinct types (ocean, ships, and land) with their influences on cloud water composition examined and implications of wet deposition discussed. Chemical analysis of cloud water samples indicates a wide pH range between 2.92 and 7.58, with an average as 4.46. The highest pH values were observed north of San Francisco, coincident with the strongest land mass influence (e.g. Si, B, and Cs). Conversely, the lowest pH values were observed south of San Francisco where there is heavy ship traffic, resulting in the highest concentrations of sulfate, nitrate, V, Fe, Al, P, Cd, Ti, Sb, P, and Mn. The acidic cloud environment with influences from various air mass types can affect the California coastal aquatic ecosystem since it can promote the conversion of micronutrients to more soluble forms. Beyond characterization of how regional air mass sources affect cloud water composition, aircraft cloud water collection provides precious information on tracking cloud processing with specific species such as oxalic acid, which is the most abundant dicarboxylic acid in tropospheric aerosols. Particular attention is given to explore relationship between detected metals with oxalate aqueous-phase production mechanisms. A number of case flights show that oxalate concentrations drop by nearly an order of magnitude relative to samples in the same vicinity with similar environmental and cloud physical conditions. Such a unique feature was consistent with an inverse relationship between oxalate and Fe. In order to examine the hypothesis that oxalate decreasing is potentially related to existing of Fe, chemistry box model simulations were conducted. The prediction results show that the loss of oxalate due to the photolysis of iron oxalato complexes is likely a significant oxalate sink in the study region due to the ubiquity of oxalate precursors, clouds, and metal emissions from ships, the ocean, and continental sources.
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Kalsi, Hardeep Singh. "Numerical modelling of shock wave boundary layer interactions in aero-engine intakes at incidence." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/284394.
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Aero-engine intakes play a critical role in the performance of modern high-bypass turbofan engines. It is their function to provide uniformly distributed, steady air flow to the engine fan face under a variety of flow conditions. However, during situations of high incidence, high curvature of the intake lip can accelerate flow to supersonic speeds, terminating with a shock wave. This produces undesirable shock wave boundary layer interactions (SWBLIs). Reynolds-Averaged Navier Stokes (RANS) turbulence models have been shown to be insensitive to the effects of boundary layer relaminarisation present in these highly-accelerated flows. Further, downstream of the SWBLI, RANS methods fail to capture the distorted flow that propagates towards the engine fan face. The present work describes simulations of a novel experimental intake rig model that replicates the key physics found in a real intake- namely acceleration, shock and SWBLI. The model is a simple geometric configuration resembling a lower intake lip at incidence. Simulations are carried out at two angles of attack, $\alpha=23^{\circ}$ and $\alpha=25^{\circ}$, with the more aggressive $\alpha=25^{\circ}$ possessing a high degree of shock oscillation. RANS, Large Eddy Simulations (LES) and hybrid RANS-LES are carried out in this work. Modifications to the one-equation Spalart-Allmaras (SA) RANS turbulence model are proposed to account for the effects of re-laminarisation and curvature. The simulation methods are validated against two canonical test cases. The first is a subsonic hump model where RANS modifications give a noticeable improvement in surface pressure predictions, even for this mild acceleration case. However, RANS is shown to over-predict the separation size. LES performs much better here, as long as the Smagorinsky-Lilly SGS model is not used. The $\sigma$-SGS model is found to perform best, and is used to run a hybrid RANS-LES that predicts a separation bubble size within $4\%$ of LES. The second canonical test case is a transonic hump that features a normal shockwave and SWBLI. RANS performs well here, predicting shock location, surface pressure and separation with good agreement with experimental measurements. Hybrid RANS-LES also performs well, but predicts a shock downstream of that measured by experiment. The use of an improved shock sensor here is able to maintain solution accuracy. Simulations of the intake rig are then run. RANS modifications provide a significant improvement in prediction of the shock location and lip surface pressure compared to the standard SA model. However, RANS models fail to reproduce the post shock interaction flow well, giving incorrect shape of the flow distortion. Further, RANS is inherently unable to capture the unsteady shock oscillations and related flow features. LES and hybrid RANS-LES predict the shock location and SWBLI well, with the downstream flow distortion also in very good agreement with experimental measurements. LES and hybrid RANS-LES are able to reproduce the time averaged smearing of the shock which RANS cannot. However, shock oscillations in the $\alpha=25^{\circ}$ case present a particular challenge for costly LES, requiring long simulation time to obtain time averaged flow statistics. Hybrid RANS-LES offers a significant saving in computational expense, costing approximately $20\%$ of LES. The work proposes recommendations for simulation strategy for intakes at incidence based on computational cost and performance of simulation methods.
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Friedlander, David J. "Understanding the Flow Physics of Shock Boundary-Layer Interactions Using CFD and Numerical Analyses." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1367928417.
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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.
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Yentsch, Robert J. "Three-Dimensional Shock-Boundary Layer Interactions in Simulations of HIFiRE-1 and HIFiRE-2." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1384195671.
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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.
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Sartor, Fulvio. "Unsteadiness in transonic shock-wave/boundary layer interactions : experimental investigation and global stability analysis." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4705.
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Dans cette étude nous considérons l'interaction entre une onde de choc et une couche limite turbulente sur un écoulement transsonique sur une bosse d'un point de vue expérimentale et théorique.Des mesures expérimentales ont permis de montrer que l'interaction est caractérisée par la coexistence de deux fréquences caractéristiques distinctes, mais l'origine des oscillations est controversée. Des simulations numériques permettent une description de l'écoulement moyen, mais ne sont pas capables de reproduire le comportement instable de l'interaction. Nous proposons d'abord une étude de stabilité globale: une décomposition en valeurs propres de l'opérateur de Navier-Stokes linéarisé indique que l'interaction est un phénomène stable, et la dynamique de l'écoulement ne peut pas être décrite par un mode global instable.Nous considérons ensuite une approche linéarisée, où la réceptivité de l'écoulement à un forçage externe est analysée à travers une décomposition en valeurs singulières du Résolvant global. Cette nouvelle approche est proposée afin d'expliquer le processus de sélection de fréquence dans cet écoulement, et montre que l'interaction filtre et amplifie le bruit résiduel existant.La même approche est enfin appliquée sur un cas d'écoulement transsonique autour d'un profil d'aile, qui peut présenter des oscillations périodiques de l'onde de choc. La décomposition en valeurs propres de opérateur de Navier-Stokes linéarisé est capable de décrire la dynamique du choc, tandis que la décomposition en valeurs singulières du Résolvant global peut indiquer la présence des instabilité convectivesA transonic interaction between a shock wave and a turbulent boundary layer is experimentally and theoretically investigated. The configuration is a channel flow over a bump, where a shock wave causes the separation of the boundary layer and a recirculating bubble is observed downstream of the shock foot.The mean flow is experimentally investigated by means of PIV, then different techniques allows to identify the main unsteadiness of this shock-wave/boundary-layer interaction. As recognised in similar configurations, the flow presents two distinguished characteristic frequencies, whose origins are still unknown.Numerical simulations are performed solving RANS equations. Results are in good agreement with the experimental mean flow, but the approach fails to predict the unsteady. The solution of RANS equations is then considered as a base flow, and a global stability analysis is performed. Eigenvalue decomposition of the Navier-Stokes operator indicates that the interaction is stable, and the dynamics cannot be described by unstable global modes.A linearised approach based on a singular-value decomposition of the Resolvent is then proposed: the noise-amplifier behaviour of the flow is highlighted by the linearised approach. Medium-frequency perturbations are shown to be the most amplified in the mixing layer, whilst the shock wave behaves as a low-pass filter.The same approach is then applied to a transonic flow over a profile, where the flow can present high-amplitude shock oscillations. The stability analysis can describe both the buffet phenomenon when an unstable mode is present, and the convective instabilities responsible of medium-frequency unsteadiness
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Schreyer, Anne-Marie [Verfasser]. "Experimental investigations of supersonic and hypersonic shock wave/turbulent boundary layer interactions / Anne-Marie Schreyer." München : Verlag Dr. Hut, 2013. http://d-nb.info/1045126853/34.
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