Dissertations / Theses on the topic 'Turbulence Flow'
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Alves, Portela Felipe. "Turbulence cascade in an inhomogeneous turbulent flow." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/63233.
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The inhomogeneous, anisotropic turbulence downstream of a square prism is investigated by means of direct numerical simulations (DNS) and two-point statistics. As noted by Moffatt (2002) “it now seems that the intense preoccupation [...] with the problem of homogeneous isotropic turbulence was perhaps misguided” acknowledging there is now a revived interest in studying inhomogeneous turbulence. The full description of the turbulence cascade requires a two-point analysis which re- volves around the recently derived Kármán-Howarth-Monin-Hill equation (KHMH). This equation is the inhomogeneous/anisotropic analogue to the so-called Kolmogorov equation (or Kármán-Howarth equation) used in Kolmogorov’s 1941 seminal papers (K41) which are the foundation to the most successful turbulence theory to date. Particular focus is placed on the near wake region where the turbulence is anticipated to be highly inhomogeneous and anisotropic. Because DNS gives direct access to all ve- locity components and their derivatives, all terms of the KHMH can be computed directly without resorting to any simplifications. Computation of the term associated with the non-linear inter-scale transfer of energy (Π) revealed that this rate is roughly constant over a range of scales which increases (within the bounds of our database) with distance to the wake generator, provided that the orientations of the pairs of points are averaged-out on the plane of the wake. This observation appears in tandem with a near −5/3 power law in the spectra of fluctuating velocities which deteriorates as the constancy of Π improves. The constant non-linear inter-scale transfer plays a major role in K41 and is required for deriving the 2/3-law (which is real space equivalent of the −5/3). We extend our analysis to a triple decomposition where the organised motion associ- ated with the vortex shedding is disentangled from the stochastic motions which do not display a distinct time signature. The imprint of the shedding-associated motion upon the stochastic component is observed to contribute to the small-scale anisotropy of the stochastic motion. Even though the dynamics of the shedding-associated motion differs drastically from that of the stochastic one, we find that both contributions are required in order to preserve the constant inter-scale transfer of energy. We further find that the inter- scale fluxes resulting from this decomposition display local (in scale-space) combinations of direct and inverse cascades. While the inter-scale fluxes associated with the coherent motion can be explained on the basis of simple geometrical arguments, the stochastic motion shows a persistent inverse cascade at orientations normal to the centreline despite its energy appearing to be roughly isotropically distributed.
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Melotte, David John. "Superfluid turbulence." Thesis, University of Newcastle Upon Tyne, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287825.
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Faisst, Holger. "Turbulence transition in pipe flow." [S.l.] : [s.n.], 2003. http://archiv.ub.uni-marburg.de/diss/z2003/0156/.
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Zwart, Philip J. "Grid turbulence in compressible flow." Thesis, University of Ottawa (Canada), 1996. http://hdl.handle.net/10393/10207.
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The flow downstream of a grid in a wind tunnel is of considerable interest for two reasons. Theoretically, it represents a good approximation to the idealized concept of homogeneous and isotropic turbulence, and therefore provides a benchmark to evaluate various analytical theories of turbulence. On the practical side, grids and screens are used extensively in the management of turbulence in a variety of applications. Experimental studies of grid turbulence are numerous in incompressible flow but far scarcer in compressible flow. The present study considers the characteristics of grid turbulence over a range of Mach numbers, M, ranging from the essentially incompressible (M = 0.16), through the moderate subsonic ($0.16 M 0.7)$ and high subsonic $(0.7 M 1.0),$ to the supersonic (M = 1.55). The experiments comprise flow visualization, performed with the shadowgraph method, and mean and fluctuating velocity measurements, made with a laser-Doppler velocimeter. Characteristics of the flow near the grid were visualized in a demonstration nozzle using the schlieren technique. In the moderate subsonic regime, flow visualization indicated that the flow near the grid underwent major changes as M increased. The turbulence intensity and decay characteristics were also found to be influenced, which was attributed to the changes in the flow near the grid. In the high subsonic regime, an unsteady quasi-normal shock was present in the test section. This induced relatively large velocity fluctuations and anisotropic turbulence. In the supersonic regime, stationary oblique shocks generated by the grid were present throughout the test section, which interfered with the turbulence and introduced errors in the measurement technique.
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Borrero, Daniel. "Subcritical Transition to Turbulence in Taylor-Couette Flow." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53140.
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Turbulence is ubiquitous in naturally-occurring and man-made flows. Despite its importance in scientific and engineering applications, the transition from smooth laminar flow to disorganized turbulent flow is poorly understood. In some cases, the transition can be understood in the context of linear stability theory, which predicts when the underlying laminar solution will become unstable as a parameter is varied. For a large class of flows, however, this approach fails spectacularly, with theory predicting that the laminar flow is stable but experiments and simulations showing the emergence of spatiotemporal complexity. In this dissertation, the direct or subcritical transition to turbulence in Taylor-Couette flow (i.e., the flow between independently rotating co-axial cylinders) is studied experimentally. Chapter 1 discusses different scenarios for the transition to turbulence and recent advances in understanding the subcritical transition within the framework of dynamical systems theory. Chapter 2 presents a comprehensive review of earlier investigations of linearly stable Taylor-Couette flow. Chapter 3 presents the first systematic study of long-lived super-transients in Taylor-Couette flow with the aim of determining the correct dynamical model for turbulent dynamics in the transitional regime. Chapter 4 presents the results of experiments regarding the stability of Taylor-Couette flow to finite-amplitude perturbations in the form of injection/suction of fluid from the test section. Chapter 5 presents numerical investigations of axisymmetric laminar states with realistic boundary conditions. Chapter 6 discusses in detail the implementation of time-resolved tomographic particle image
velocimetry (PIV) in the Taylor-Couette geometry and presents preliminary tomographic PIV measurements of the growth of turbulent spots from finite-amplitude perturbations. The main results are summarized in Chapter 7.
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Veale, William. "Shallow flow turbulence: an experimental study." Thesis, University of Canterbury. Civil Engineering, 2005. http://hdl.handle.net/10092/1073.
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A particle tracking velocimetry (PTV) system is used to investigate the turbulent properties at the free surface of shallow shear flows and a shallow vortex street (VS) wake flow. The resolution of the PTV system enables information to be gathered regarding the large-scale turbulent structure of these flows, and also enables analysis to proceed in both the temporal and spatial domains. Statistical tools such as the probability density function (PDF), autocorrelation and power spectral density (PSD) are utilised to characterise the turbulent properties at the flow surface. Two supercritical flows and one subcritical shallow shear flow are analysed. Taylor's frozen turbulence hypothesis is shown to be valid for these flows, and the integral length scales indicate that 2D isotropic structures with scales larger than the flow depth are present at the free surface. Such large-scale structures at the free surface are consistent with observations from dye visualisation experiments and with "spiral eddies" identified by Kumar, et al (1998). The longitudinal extent of near and intermediate wake fields for the shallow VS wake flow is well defined by the integral wake length scale specified by v.Carmer (2005). The near wake region is characterised by high rates of exchange between the mean flow and large-scale 2D coherent structures (2DCS). In the intermediate field, the rate of decay of the turbulent stress components greatly diminishes as the 2DCS are stabilised and dissipated under the action of bed friction. Multiple peaks are observed in the power spectral density of the turbulent fluctuations. The periodic shedding of 2DCS behind the circular cylinder is characterised by an energy peak at a Strouhal number of 0.21, and further energy peaks are observed in the near-wake region. The PSD estimates are consistent with the findings of v.Carmer (2005) in which a -5/3 decay law to high frequencies is observed, and no evidence of an inverse energy cascade is present.
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Teixeira, Jose Carlos Fernandes. "Turbulence in annular two phase flow." Thesis, University of Birmingham, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.570318.
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The structure of turbulent flow in vertical upwards annular air water two-phase flow was examined. Experiments were carried out in a 32 mm internal diameter tube using laser Doppler anemometry. Simultaneous measurements of the two velocity components and the Reynolds stress were obtained by the use of two colours (blue and green) of a 50 mW argon ion laser. The gas core was seeded by polystyrene particles of 1 um diameter which were believed to follow the gas turbulent fluctuations. The characteristics of the signal were used to discriminate these tracer particles from the water droplets. The gas velocity profiles were shown to be more peaked at the centre of the tube than those observed in turbulent single phase flow. Comparative analysis with other data suggested that both interfacial roughness and, particularly, the momentum interchange between the droplets and the gas core, are the most important factors affecting the gas velocity profile in annular flow. Turbulent fluctuations of the gas velocity were found to be significantly higher than those typical of single phase flow, for similar gas Reynolds numbers. The interfacial shear, droplet size and concentration and the presence of disturbance waves at the interface were identified as being the most important factors affecting the gas turbulence in annular flow. A model was developed to predict the axial component of the turbulent fluctuations at the centre of the tube. The turbulence transport properties were observed to differ from those typical of single phase flow: i.e., higher production of turbulent energy (associated with higher anisotropy ratios), higher turbulence length scales and comparativelly lower dissipation ratios. Extrapolation of the mixing length theory to annular flow appeared to be inappropriate. Droplet size measurements showed that the gas velocity and the droplet concentration are the most important parameters affecting droplet size. At low droplet concentrations (where the gas-droplet interaction is more important than that between the droplets), a modified Weber number based on the homogeneous gas core momentum describes the maximum droplet diameter. At high droplet concentrations, the data suggests that coalescence is the dominant factor. Droplet velocity was found to be related to the size of the droplets: i.e., large droplets travel slower than small ones. The difference in velocity between large and small droplets was found to depend on the liquid and gas flow rates. This observation is related to conditions where droplet coalescence occurs. The effect of inserts on droplet size and the entrained fraction was examined. Disturbances in the channel geometry were found to affect the mean droplet size due to the creation of a new droplet population. The entrained fraction of liquid downstream of the insert was also affected. A model was formulated to describe the liquid interchange in the presence of a vertical plate.
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Wu, Jiunn-Chi. "A study of unsteady turbulent flow past airfoils." Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/13091.
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Frohnapfel, Bettina M. [Verfasser]. "Flow Control of Near-Wall Turbulence : Strömungskontrolle wandnaher Turbulenz / Bettina M Frohnapfel." Aachen : Shaker, 2007. http://d-nb.info/1166511243/34.
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Dallas, Vassilios. "Multiscale structure of turbulent channel flow and polymer, dynamics in viscoelastic turbulence." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/5855.
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This thesis focuses on two important issues in turbulence theory of wall-bounded flows. One is the recent debate on the form of the mean velocity profile (is it a log-law or a power-law with very weak power exponent?) and on its scalings with Reynolds number. In particular, this study relates the mean flow profile of the turbulent channel flow with the underlying topological structure of the fluctuating velocity field through the concept of critical points, a dynamical systems concept that is a natural way to quantify the multiscale structure of turbulence. This connection gives a new phenomenological picture of wall-bounded turbulence in terms of the topology of the flow. This theory validated against existing data, indicates that the issue on the form of the mean velocity profile at the asymptotic limit of infinite Reynolds number could be resolved by understanding the scaling of turbulent kinetic energy with Reynolds number. The other major issue addressed here is on the fundamental mechanism(s) of viscoelastic turbulence that lead to the polymer-induced turbulent drag reduction phenomenon and its dynamical aspects. A great challenge in this problem is the computation of viscoelastic turbulent flows, since the understanding of polymer physics is restricted to mechanical models. An effective numerical method to solve the governing equation for polymers modelled as nonlinear springs, without using any artificial assumptions as usual, was implemented here for the first time on a three-dimensional channel flow geometry. The superiority of this algorithm is depicted on the results, which are much closer to experimental observations. This allowed a more detailed study of the polymer-turbulence dynamical interactions, which yields a clearer picture on a mechanism that is governed by the polymer-turbulence energy transfers.
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Kevlahan, Nicholas Keville-Reynolds. "Structure and shocks in turbulence." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321033.
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Lu, Youyu. "Flow and turbulence in a tidal channel." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0007/NQ34275.pdf.
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Agarwal, Akshat. "Breakdown to turbulence in non-Newtonian flow." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/43851.
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Transition to turbulence in polymeric channel flow is investigated, with the FENE-P model used to characterize the viscoelastic behaviour of the flow. Simulations are performed to study transition through both the natural and bypass routes. In the linear growth regime of natural transition, differences in the growth rate of a TS wave are explained by appealing to the production of the perturbation energy budget. At high Weissenberg number, the growth rate is substantially lower in comparison to Newtonian flow. As a result, the transition process is prolonged. Upon the introduction of three dimensional disturbances, Newtonian and non-Newtonian cases undergo transition through the H-type instability. The spanwise extent of the lambda structures during transition is larger in non-Newtonian flow. Bypass transition is initiated by an initially-localized disturbance. In the linear growth regime, the flow response is stabilized by viscoelasticity, and the maximum attainable disturbance-energy amplification is reduced with increasing polymer concentration. The reduction in the energy growth rate is attributed to the polymer work, which plays a dual role: First, a spanwise polymer-work term develops, and is explained by the tilting action of the wall-normal vorticity on the mean streamwise conformation tensor. This resistive term weakens the spanwise velocity perturbation thus reducing the energy of the localized disturbance. The second action of the polymer is analogous, with a wall-normal polymer work term that weakens the vertical velocity perturbation. Its indirect effect on energy growth is substantial since it reduces the production of Reynolds shear stress and in turn of the streamwise velocity perturbation, or streaks. During the early stages of non-linear growth, the dominant effect of the polymer is to suppress the large scale streaky structures which are strongly amplified in Newtonian flows. As a result, the process of transition to turbulence is prolonged and, after transition, a drag reduced turbulent state is attained.
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Riahi, Ardeshir. "Turbulent swirling flow in short cylindrical chambers." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30810.
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The effects of aspect ratio (L/D) on the rate of decay of swirl in a cylindrical chamber were experimentally studied using the Laser-Doppler-Anemometry technique. Preliminary measurements revealed that water should be used as working fluid; the results pertaining to air were inferred from Reynolds number similarity.
The steady-state measurements revealed that a solid body type of rotation can be generated by a disc whose surface has been uniformly roughened. The effect of aspect ratio on the rate of decay of such flow field was studied in three chambers with aspect ratios in the range of interest to engine combustion. Experimental results showed a faster decay rate in the shorter chamber (i.e. smaller aspect ratio). This was attributed to the stronger swirl driven secondary flow pattern in the shorter chamber.
A mathematical model describing axi-symmetric, decaying, turbulent swirling flow inside a short cylindrical chamber was also developed. The model was numerically solved, using the control-volume analysis, to provide insight on swirl decay in engines. The model validation was based on experimental observations.
Turbulence parameters were represented by a two-equation turbulence model, modified for streamline curvature effects. The ad-hoc curvature modification of the standard k-e model proposed by Launder et al. and the mixing energy model developed by Saffman-Wilcox-Traci (SWT) were used to account for curvature effects. The analysis of steady flow between two long concentric cylinders, established the superiority of the latter over the former method. The SWT model was also successfully used in reproducing previously published experimental results, pertaining to decaying swirling flow field (mean velocity and turbulence intensity) in a short cylinder. The calculated turbulence intensity profile revealed that swirl promotes anisotropic turbulence.
The validated numerical model was used to predict the effect of aspect ratio on the rate of decay of the flow field observed by the experimental measurements in the present study. The overall prediction of decay rate was successful, leading to the conclusion that Wilcox and Chambers model can be used in predicting the behaviour of two-dimensional transient turbulent swirling flows.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
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Meleschi, Shangari B. "Ultrasonic technique in determination of grid-generated turbulent flow characteristics and caustic formation." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0429104-153706.
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Grigoriev, Igor. "Turbulence modeling of compressible flows with large density variation." Doctoral thesis, KTH, Turbulens, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-183452.
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In this study we highlight the influence of mean dilatation and mean density gradient on the Reynolds stress modeling of compressible, heat-releasing and supercritical turbulent flows.Firstly, the modeling of the rapid pressure-strain correlation has been extended to self-consistently account for the influence of mean dilatation.Secondly, an algebraic model for the turbulent density flux has been developed and coupled to the tensor equationfor Reynolds stress anisotropy via a 'local mean acceleration',a generalization of the buoyancy force. We applied the resulting differential Reynolds stress model (DRSM) and the corresponding explicit algebraic Reynolds stress model (EARSM) to homogeneously sheared and compressed or expanded two-dimensional mean flows. Both formulations have shown that our model preserves the realizability of the turbulence, meaning that the Reynolds stresses do not attain unphysical values, unlike earlier approaches. Comparison with rapid distortion theory (RDT) demonstrated that the DRSM captures the essentials of the transient behaviour of the diagonal anisotropies and gives good predictions of the turbulence kinetic energy. A general three-dimensional solution to the coupled EARSM has been formulated. In the case of turbulent flow in de Laval nozzle we investigated the influence of compressibility effects and demonstrated that the different calibrations lead to different turbulence regimes but with retained realizability. We calibrated our EARSM against a DNS of combustion in a wall-jet flow. Correct predictions of turbulent density fluxes have been achieved and essential features of the anisotropy behaviour have been captured.The proposed calibration keeps the model free of singularities for the cases studied. In addition, we have applied the EARSM to the investigation of supercritical carbon dioxide flow in an annulus. The model correctly captured mean enthalpy, temperature and density as well as the turbulence shear stress. Hence, we consider the model as a useful tool for the analysis of a wide range of compressible flows with large density variation.QC 20160314
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Quinn, Brenda E. "Rossby wave, drift wave and zonal flow turbulence." Thesis, University of Warwick, 2011. http://wrap.warwick.ac.uk/51779/.
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An extensive qualitative and quantitative study of Rossby wave, drift wave and zonal flow turbulence in the Charney-Hasegawa-Mima model is presented. This includes details of two generation mechanisms of the zonal flows, evidence of the nonlocal nature of this turbulence and of the energy exchange between the small and large scales. The modulational instability study shows that for strong primary waves the most unstable modes are perpendicular to the primary wave, which corresponds to the generation of a zonal flow if the primary wave is purely meridional. For weak waves, the maximum growth occurs for off-zonal modulations that are close to being in three-wave resonance with the primary wave. Nonlinear jet pinching is observed for all nonlinearity levels but the subsequent dynamics differ between strong and weak primary waves. The jets of the former further roll up into Kármán-like vortex streets and saturate, while for the latter, the growth of the unstable mode reverses and the system oscillates between a dominant jet and a dominant primary wave. A critical level of nonlinearity is defined which separates the two regimes. Some of these characteristics are captured by truncated models. Numerical proof of the extra invariant in Rossby and drift wave turbulence is presented. While the theoretical derivations of this invariant stem from the wave kinetic equation which assumes weak wave amplitudes, it is shown to be relatively-well conserved for higher nonlinearities also. Together with the energy and enstrophy, these three invariants cascade into anisotropic sectors in the k-space as predicted by the Fjørtoft argument. The cascades are characterised by the zonostrophy pushing the energy to the zonal scales. A small scale instability forcing applied to the model has demonstrated the wellknown drift wave - zonal flow feedback loop. The drift wave turbulence is generated from this primary instability. The zonal flows are then excited by either one of the generation mechanisms, extracting energy from the drift waves as they grow. Eventually the turbulence is completely suppressed and the zonal flows saturate. The turbulence spectrum is shown to diffuse in a manner which has been mathematically predicted. The insights gained from this simple model could provide a basis for equivalent studies in more sophisticated plasma and geophysical fluid dynamics models in an effort to fully understand the zonal flow generation, the turbulent transport suppression and the zonal flow saturation processes in both the plasma and geophysical contexts.
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Stewart, Mark Thomas. "Turbulence structure of rough-bed open-channel flow." Thesis, University of Aberdeen, 2014. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=210848.
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Open-channel flows are ubiquitous in nature and play a central role in many hydraulic engineering problems. This flow type occurs almost exclusively under fully-rough turbulent conditions and it is not uncommon for the relative submergence of these flows to be low. Despite this, most theory has so far been developed for smooth wall flows or rough-bed flows at high submergence while its applicability at low relative submergence remains questionable. This thesis therefore aims to contribute towards an improved understanding of turbulence structure in rough-bed open-channel flow at low to intermediate relative submergence. Experiments were conducted to collect turbulent velocity field data for nine different flow scenarios, covering roughness Reynolds numbers between 175 and 900, and relative submergence between 2.5 and 7.5. Each flow scenario was measured independently using particle image velocimetry (PIV) in five distinct configurations. The PIV system was first configured to make two-component velocity measurements with a very wide field of view (up to twenty flow depths) along the channel centreline in a streamwise-wall-normal plane. These measurements were supplemented with three-component stereoscopic PIV recordings along the same plane albeit with a shorter field of view. The third, fourth and fifth set ups involved stereoscopic PIV in three separate transverse-wall-normal planes and thus ensured the complete lateral coverage of the flow field from the sidewall to the centreline. The four-camera arrangement of each of the present stereoscopic PIV configurations was exploited to obtain velocity field statistics with significantly reduced contributions from measurement noise. The thesis reports distributions of bulk velocity statistics and spectra of all three velocity components. In addition, characteristic large scale features of the instantaneous flow are examined using velocity field visualisation, two-point velocity correlations and premultiplied velocity spectra. Further analysis is carried out on the time-averaged flow field to visualise secondary current patterns and to study their lateral extent.
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Collier, James D. "Investigating strong flow-turbulence dynamics via numerical simulations." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/77692/.
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In a magnetically confined fusion plasma, small scale instabilities drive the anomalous transport which determines the confinement. It is possible for the plasma in a tokamak to have a toroidal rotation, either formed spontaneously or by being given some external drive. This rotation may help improve confinement. Therefore, this thesis aims to investigate the effects of strongly rotating plasmas, with toroidal Mach number approaching unity, on the turbulence dynamics in numerical simulations. For this purpose, the global gyrokinetic PIC code ORB5 has been extended to include these strong- flow terms; retaining the background E x B drift terms typically neglected. Investigations into GAMs appearing as eigenfunctions with forms similar to the Airy function found that although the behaviour of GAMs with increasing radial wavenumber were poorly predicted, eigenfunctions of the predicted form were still found. As radial wavenumber increased the eigenfunctions became less well defined. Linear simulations with a solid-body rotation found that the frequency of the GAMs and toroidal modes with n n = 0 exhibited an increase for larger magnitude of toroidal velocity and were largely independent of direction of rotation. Further studies found that an increasing toroidal rotation initially showed a destabilization effect on the linear modes, acting against the stabilizing effects of already present gradient profile flows, before beginning to reduce the mode growth at large toroidal velocities. This behaviour was found to be largely reflected in the tilting of the mode structures caused by rotation. A stabilizing effect was also observed in collisionless non-linear simulations. The presence of a positively rotating plasma gave reductions to turbulence, but a much stronger turbulence suppression was found when the plasma was rotated in the opposite direction. It is suspected that the large ows caused by the equilibrium profile gradients give rise to some of this observed asymmetry.
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Klymak, Jody Michael. "Stratified flow and turbulence over an abrupt sill /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/10982.
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Chen, Xu. "New formulation of optical flow for turbulence estimation." Thesis, Ecully, Ecole centrale de Lyon, 2015. http://www.theses.fr/2015ECDL0025/document.
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Le flot optique est un outil, prometteur et puissant, pour estimer le mouvement des objets de différentes natures, solides ou fluides. Il permet d’extraire les champs de vitesse à partir d’une séquence d’images. Dans cette étude, nous développons la méthode du flot optique pour récupérer, d’une manière précise, le champ de vitesse des mouvements turbulents incompressibles. L’estimation de turbulence consiste à minimiser une fonction d’énergie composée par un terme d’observation et un terme de régularisation. L’équation de transport d’un scalaire passif est alors employée pour représenter le terme d’observation. Cependant, dans le cas où le nombre de Reynolds est grand, et, à cause des contraintes optiques, l’image n’est pas pleinement résolue pour prendre en compte la physique de toutes les échelles de la turbulence. Pour compléter les informations manquantes liées aux physiques des petites échelles, nous adoptons une démarche similaire à celle de Large Eddy Simulation (LES), et, proposons d’utiliser le modèle mixte afin de tenir compte de l’interaction entre les grandes échelles et celles non-résolues. Quant au terme de régularisation, il se repose sur l’équation de continuité des fluides incompressibles. Les tests à l’aide des images synthétiques et expérimentales de la turbulence bi-dimensionnelle - des données des cas test de la communauté du flot optique -, ont non seulement validé notre démarche, mais montrent une amélioration significative des qualités des champs de vitesses extraites. Le cas du flot optique, en 3D, relève encore du défi dans le cas de l’estimation des champs de vitesse de la turbulence. D’une part, contrairement au 2D où il existe des cas tests bien établis, il n’existe pas, à notre connaissance, des séquences d’images 3D référentielles permettant de tester notre démarche et méthode. D’autre part, l’augmentation du coût d’estimation demande des algorithme adaptés. Ainsi, nous sommes amené à utiliser la simulation numérique directe d’écoulement turbulent en présence d’un scalaire passif, pour générer des données de scalaires afin d’évaluer la performance du flot optique. Nous prêtons également attention à l’effet du nombre de Schmidt qui caractérise la relation entre la diffusion moléculaire scalaire et la dissipation de turbulence. Les tests sont ensuite effectués avec cette base de données numériques. Les résultats montrent que la précision de l’estimation augmente avec des nombres de Schmidt plus élevés. Par ailleurs, l’influence du terme de régularisation est aussi étudié au travers deux équations qui se différencient par l’ordre spatial des dérivées partielles. Les résultats numériques montrent que l’équation avec un terme de régularisation de seconde-ordre est meilleure que celle de premier-ordreThe method of optical flow is a powerful tool for motion estimation. It is able to extract the dense velocity field from image sequence. In this study, we employ this method to retrieve precisely the incompressible turbulent motions. For 2D turbulence estimation, it consists in minimizing an objective function constituted by an observation term and a regularization one. The observation term is based on the transport equation of a passive scalar field. For non-fully resolved scalar images, we propose to use the mixed model in large eddy simulation (LES) to determine the interaction between large-scale motions and the unresolved ones. The regularization term is based on the continuity equation of 2D incompressible flows. Evaluation of the proposed formulation is done over synthetic and experimental images. In addition, we extend optical flow to three dimensional and multiple scalar databases are generated with direct numerical simulation (DNS) in order to evaluate the performance of optical flow in the 3D context. We propose two formulations differing by the order of the regularizer. Numerical results show that the formulation with second-order regularizer outperforms its first-order counterpart. We also draw special attention to the effect of Schmidt number, which characterizes the ratio between the molecular diffusion of the scalar and the dissipation of the turbulence. Results show that the precision of the estimation increases as the Schmidt number increases. Overall, optical flow has showcased its capability of reconstructing the turbulent flow with excellent accuracy. This method has all the potential and attributes to become an effective flow measurement approach in fluid mechanics community
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Selvam, Kamal. "Transition to turbulence in circular expansion pipe flow." Thesis, Normandie, 2017. http://www.theses.fr/2017NORMLH32/document.
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La thèse traite de recherches numériques et expérimentales sur l’écoulement à traves des conduites circulaires ou des tubes avec une petite entrée et un diamètre de sortie plus grand, parfois appelées élargissement ou divergents. L’écoulement dans un élargissement est globalement stable pour des nombres de Reynolds élevés. Ainsi la simulation numérique de ce type d’écoulement nécessite de grands domaines de calcul contenant la zone de recirculation, qui croît linéairement. En outre, les études expérimentales dans les élargissements brusques indiquent que la transition se produit à des nombres de Reynolds plus faibles que prévue par la théorie linéaire de stabilité. La raison pour cette transition précoce est due à la présence d’imperfections dans le dispositif expérimental, qui agit comme une perturbation d’amplitude finie de l’écoulement. Des simulations numériques directes des équations de Navier-Stokes ont été réalisées avec deux types différents de perturbations (i) l’inclination et (ii) le vortex. Tout d’abord, la perturbation de type inclinaison, qui est appliqué à l’entrée, crée une zone de recirculation asymétrique, puis se casse pour former une turbulence localisée en aval de l’expansion. Deuxièmement, la perturbation de type vortex, crée des structures qui ressemblent à un mode azimutal d’ordre inférieur, déjà identifié comme une perturbation optimale amplifiée. Il croît en raison de l’instabilité convective, puis forme une tâche de turbulence localisée. Enfin, la corrélation spatiale et la décomposition en modes propres révèlent que cette turbulence localisée obtient son énergie de l’écoulement d’entréeThe thesis deals with numerical and experimental investigations of flow through circular pipes with smaller inlet and larger outlet diameter, also known as expansion pipes. The hydrodynamic expansion pipe flow is globally stable for high Reynolds number. In order to numerically simulate these types of flows, large computational domains that could accommodate the linearly growing symmetric recirculation region is needed. Moreover, experimental studies of expansion pipe flows indicate that the transition occurs at lower Reynolds number than predicted by the linear stability theory. The reason for early transition is due to the presence of imperfections in the experimental setup, which acts as a finite-amplitude perturbation of the flow. Three-dimensional direct numerical simulations of the Navier-Stokes equations with two different types of perturbations (i) the tilt and (ii) the vortex are investigated. First, the tilt perturbation, which applied at the inlet, creates an asymmetric recirculation region and then breaks to form localised turbulence downstream the expansion section. Second, the vortex perturbation, creates structures that looks like lower order azimuthal mode, resembles an optimally amplified perturbation. It grows due to convective instability mechanism and then breaks to form localised turbulence. Spatial correlation and the proper orthogonal decomposition reveal that this localised turbulence gains it energy from the core flow coming out of the inlet pipe
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Horton, Nial. "Influence of a turbulent stream flow on the subsurface flow through a regular porous matrix." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources, 2008. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=25938.
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Jaafar, Abdul Aziz. "Flow and heat transfer in a rotating cavity with a stationary casing." Thesis, University of Bath, 2000. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311453.
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Birch, N. T. "Turbulence and transition modelling in turbomachinery flows." Thesis, Cranfield University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379491.
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Yan, Zheng. "Turbulence-driven shear flow and self-regulating drift wave turbulence in a cylindrical plasma device." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3338840.
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Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed Jan. 13, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 129-132).
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Neroorkar, Kshitij D. "Numerical study of turbulence transition models." Birmingham, Ala. : University of Alabama at Birmingham, 2007. https://www.mhsl.uab.edu/dt/2007m/neroorkar.pdf.
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Weber, Francis J. "Ultrasonic beam propagation in turbulent flow." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0419104-173917.
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Connell, R. J. "Unstable equilibrium : modelling waves and turbulence in water flow." Diss., Lincoln University, 2008. http://hdl.handle.net/10182/592.
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This thesis develops a one-dimensional version of a new data driven model of turbulence that uses the KL expansion to provide a spectral solution of the turbulent flow field based on analysis of Particle Image Velocimetry (PIV) turbulent data. The analysis derives a 2nd order random field over the whole flow domain that gives better turbulence properties in areas of non-uniform flow and where flow separates than the present models that are based on the Navier-Stokes Equations. These latter models need assumptions to decrease the number of calculations to enable them to run on present day computers or super-computers. These assumptions reduce the accuracy of these models. The improved flow field is gained at the expense of the model not being generic. Therefore the new data driven model can only be used for the flow situation of the data as the analysis shows that the kernel of the turbulent flow field of undular hydraulic jump could not be related to the surface waves, a key feature of the jump. The kernel developed has two parts, called the outer and inner parts. A comparison shows that the ratio of outer kernel to inner kernel primarily reflects the ratio of turbulent production to turbulent dissipation. The outer part, with a larger correlation length, reflects the larger structures of the flow that contain most of the turbulent energy production. The inner part reflects the smaller structures that contain most turbulent energy dissipation. The new data driven model can use a kernel with changing variance and/or regression coefficient over the domain, necessitating the use of both numerical and analytical methods. The model allows the use of a two-part regression coefficient kernel, the solution being the addition of the result from each part of the kernel. This research highlighted the need to assess the size of the structures calculated by the models based on the Navier-Stokes equations to validate these models. At present most studies use mean velocities and the turbulent fluctuations to validate a models performance. As the new data driven model gives better turbulence properties, it could be used in complicated flow situations, such as a rock groyne to give better assessment of the forces and pressures in the water flow resulting from turbulence fluctuations for the design of such structures. Further development to make the model usable includes; solving the numerical problem associated with the double kernel, reducing the number of modes required, obtaining a solution for the kernel of two-dimensional and three-dimensional flows, including the change in correlation length with time as presently the model gives instant realisations of the flow field and finally including third and fourth order statistics to improve the data driven model velocity field from having Gaussian distribution properties. As the third and fourth order statistics are Reynolds Number dependent this will enable the model to be applied to PIV data from physical scale models. In summary, this new data driven model is complementary to models based on the Navier-Stokes equations by providing better results in complicated design situations. Further research to develop the new model is viewed as an important step forward in the analysis of river control structures such as rock groynes that are prevalent on New Zealand Rivers protecting large cities.
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Lagha, Maher. "Modeling the transition to turbulence in plane Couette flow." Phd thesis, Ecole Polytechnique X, 2006. http://pastel.archives-ouvertes.fr/pastel-00675068.
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The Galerkin method is used to derive a realistic model of plane Couette flow in terms of partial differential equations governing the space-time dependence of the amplitude of a few cross-stream modes. Numerical simulations show that it reproduces the globally sub-critical behavior typical of this flow. In particular, the statistics of turbulent transients at decay from turbulent to laminar flow displays striking similarities with experimental findings.
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Hunt, Alan Ernest. "The behaviour of turbulence in unsteady open channel flow." Thesis, University of Canterbury. Civil Engineering, 1997. http://hdl.handle.net/10092/7722.
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An investigation into the behaviour of the turbulence during laboratory simulations of floods in rivers with mild bed slopes was undertaken. Computer control of the flow rate into the flume enabled reproducible flood waves to be generated. To rigorously model the energy gradients in a long channel, an interactive sluice gate control was developed for the downstream end of the flume. Mean flow unsteadiness effects on the turbulence were evaluated by considering different duration hydrographs with similar shapes and magnitudes. The investigation was limited to the longitudinal component of turbulence, as a one-component laser Doppler anemometer was employed for the determination of point velocities. Flow visualisation using a dye plume supplemented velocity data. It was observed that for events having a shorter duration the peak turbulent intensity had a greater magnitude, and occurred relatively earlier on the rising limb of the flood.
The turbulent energy peak coincided with the maximum flow rate divergence. For increasing flow divergence magnitude, which only occurs on the rising limb, the production of turbulence was larger than dissipation, with the transport of turbulence providing an additional sink for turbulent energy. After the depth had peaked the flow experienced pseudo-equilibrium conditions, where the transport mechanism was insignificant and the rate of production approximated dissipation. A feature of the falling limb was a period of inactivity, in which the magnitudes of production and dissipation were at minimum.
A second -5/3 slope region was observed in the energy spectra. The length scale associated with an energy source for this double structure was two orders of magnitude larger than the Kolmogorov dissipation length scale. Decay times for flow structures of this size are similar to the duration of these hydrographs.
It is possible that the unsteady flow created vortex structures that persisted for some time after the flow which generated them had moved downstream. These vortex structures, which provide a turbulence memory mechanism, and the state of pseudo-equilibrium on the falling limb are responsible for residual turbulent energy in the flow throughout the falling limb and immediately following the passing of the flood wave.
In addition, it is suggested that mean flow controls both the production and dissipation of turbulence, with the dissipation of turbulent kinetic energy being controlled by the diffusion of momentum during low speed streaks. The Kolmogorov scale may be interpreted as defining the critical damping condition along these streaks where Reynolds stresses balance viscous forces.
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Courts, Samuel Scott. "Superfluid turbulence in two-fluid flow of helium II /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu148759165817599.
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Schneider, Gerald Manfred. "Structures and turbulence characteristics in a precessing jet flow /." Title page, contents and summary only, 1996. http://web4.library.adelaide.edu.au/theses/09PH/09phs358.pdf.
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Vanderwel, Christina M. "Turbulent Diffusion in Uniformly Sheared Flow." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31806.
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The objective of this thesis research is to further the understanding of turbulent diffusion by experimentally studying the turbulent diffusion of a plume of dye released in uniformly sheared flow generated in a water tunnel. The flow studied was nearly homogeneous but strongly anisotropic and had a turbulent Reynolds number of 150. Maps of the turbulent velocity and dye concentration were measured simultaneously using stereoscopic particle image velocimetry and planar laser-induced fluorescence. A thorough analysis of the planar laser-induced fluorescence technique was performed; several previously unconsidered sources of error were identified and corrections were proposed. The measured evolutions of the mixed velocity-concentration statistics of the plume were compared with previous studies. The turbulent scalar flux vector was related to the mean concentration gradient through a first-order gradient transport model and, for the first time in an experimental flow, all components of the turbulent diffusivity tensor were measured directly. The turbulent diffusivity tensor was found to be highly anisotropic and its streamwise component appeared to be counter-gradient. The relative diffusion of the plume was also investigated and the evolution of the mean square particle separation was found to be consistent with Richardson-Obukhov scaling, with a value of Richardson's constant equal to 0.35. The fine structure of the concentration field and the mixed velocity-concentration statistics were also documented. Because of the high level of intermittency of the present plume, the scalar probability density function was strongly non-Gaussian and the conditional expectations of the velocity components and the scalar dissipation, conditioned upon the scalar value, were distinctly non-linear. Lastly, the role of coherent structures on scalar diffusion was investigated and a conditional eddy analysis demonstrated that hairpin vortices were associated closely with large scalar flux events.
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Othman, Faridah. "Flow modelling in compound channels." Thesis, University of Newcastle Upon Tyne, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327324.
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Medina, Enriquez Pablo. "Start of sediment mtion and resuspension in turbulent flows: applications of zero-mean flow grid stirred turbulence on sediment studies." Doctoral thesis, Universitat Politècnica de Catalunya, 2002. http://hdl.handle.net/10803/6384.
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The objectives of the thesis were, on the one hand, to test the possibilities of a well-known experimental configuration (oscillating grid mixing box), used to study stratified fluids in turbulent flows with zero-mean, on the study of sediment transport, and to find out what aspects involved in this phenomena could be explored from this new perspective. On the other hand, compare a well-established criterion, such as Shields parameter, with the local turbulent energy ( ), as well as to compare the differences between zero-mean and sheared induced lift-off.Verification and adjustments to the parameterizations given in the bibliography for the r.m.s. turbulent velocity, , generated by an oscillating grid were done as well as the calibration of the different mixing boxes and grids to be used through a series of experiments. This gave a clear view of the behaviour of the flow in all the mixing boxes used.
A special experimental configuration was designed and performed for the first time, and measurements were taken to get to know the flow properties in the region between the grid and the bottom (solid boundary). Experiments were performed with actual sediment with different characteristics, for instance, different sediment sizes (from clay to medium sands) including samples made of single sediment size and samples extracted from the seabed. An experiment to compare the sediment behaviour under a sheared flow (recirculation tank) and under a no-sheared flow (oscillating grid mixing box) was designed and performed.
The present work concluded that the experimental configuration used could be employed in further works to investigate aspects of sediment transport under a turbulent flow with great accuracy. This experimental configuration, in combination with techniques of image analysis, greatly improves the capabilities of the grid stirred experimental configurations, mainly on the study of sediment behaviour. The flow behaviour, between the grid and the free surface, and between the grid and the bottom, is, in general terms, the same. Other important contributions of the present work are the measurements taken near the boundary. Vortices do not distort before impingement. After vortex impingement, no constant mean flow is distinguished. The former enhanced the idea that these experimental configurations are suitable for studying the behaviour of a sediment bed under the influence of a turbulent flow. A smaller magnitude of than of was required to start sediment motion, through comparing the theoretical critical friction velocity, (Critical Shields Parameter), needed to start sediment motion with the measured critical for different sediment sizes. The results obtained show the importance that the time span between extraction and analysis has on the measured value of , and that cohesiveness of sediment play a more important role than sediment size hampering the erosion processes that cause sediment lift off from the sediment bed. Under the same circumstances, a turbulent flow is more efficient than eroding the sediment bed, since it does not depend on the roughness of the sediment bed. It was possible to measure sediment velocities during lift-off and settling, using grid stirred experimental configurations in conjunction with image analysis techniques. It is even possible to determine the sediment size (size mode), even in the range of clays and silts, with an error as small as 6 or 8 percent. It was possible to quantify the sediment flux at a given turbulence intensity. Velocity fluctuations are about the same in the three directions and in a random way above the sediment bed, meaning no preferential direction of stresses. The former hampers the process of particle imbrication making it easier to dislocate the particles from the bed.
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Franceschini, Lucas. "Modeling Strategies for Aerodynamic Flow Reconstruction from partial measurements." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX092.
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Dans un premier temps, nous nous intéresserons à la récupération du champ moyen à partir d'informations partielles ou éparses, allant des sondes de vitesse ponctuelles à la pression ou frottement de paroi. Pour le réaliser, on considère les équations de Reynolds-Averaged Navier-Stokes (RANS), complétées par un modèle, ici le Spalart-Allmaras. Ce type de modélisation a été conçu pour quelques configurations d'écoulement de référence et peut manquer de généralité, ce qui conduit à des prédictions erronées, surtout lorsqu'il y a recirculation. Nous proposons la modification de ce modèle avec un paramètre de contrôle tel que la solution qui en découle corresponde le mieux aux données de champ moyen mentionnées ci-dessus. La configuration considérée est une marche descendente à Re=28275, avec des données réelles provenant d'un DNS.Ensuite, nous nous intéressons à l'analyse linéaire de champ moyen et à son utilisation pour prédire la fluctuation non linéaire instationnaire. En particulier, nous concevons un modèle d'ordre réduit, composé de l'équation du champ moyen couplé aux modes de résolvent, qui prédit la fluctuation pour chaque fréquence existante. Les énergies de ces modes sont utilisées comme paramètres à régler par la procédure d'assimilation des données, qui nécessite généralement (très) peu de donnée, typiquement des signaux résolus en temps issus de sondes ponctuelles. Cette technique sera appliquée dans des écoulements transitoires tels que celui autour d'un cylindre à section carrée, un cas de référence pour les écoulements oscillateurs, et un pas orienté vers l'arrière, un écoulement type d'amplificateur de bruit.Nous considérons ensuite un cas turbulent correspondant à l'écoulement autour d'un cylindre à section carrée à Re=22000, ayant à la fois des caractéristiques d'oscillateur (émission périodique de vortices) et d'amplificateur de bruit (représenté par les structures Kelvin-Helmholtz). L'analyse classique de stabilité de champ moyen est utilisée pour récupérer le mode d'emission de vortex et une technique de résolvent, basée sur les équations linéarisées autour de la composante périodique, est utilisée pour récupérer la dépendance des modes Kelvin-Helmholtz avec l'emission de vortexIn a first moment we will be interested in the recovery of the mean-flow quantities from partial or sparse information, ranging from point-wise velocity probes to wall-pressure and friction. This will be achieved by considering the Reynolds-Averaged Navier-Stokes (RANS) equations, completed with a model, here the Spalart-Allmaras. This kind of modeling has been conceived for a few benchmark flow configurations and may lack generality, leading to erroneous predictions, especially when re-circulation is present. We propose the modification of this model with a tuning parameter such that its solution matches the best the aforementioned mean-flow data. The configuration considered was a Backward-Facing Step at Re=28275, with actual data stemming from a DNS.Then, we turn our attention to linear mean-flow analysis and its use to predict the nonlinear unsteady fluctuation. In particular, we design a reduced-order model, composed by the mean-flow equation coupled with the resolvent modes, predicting the fluctuation for each existing frequency. The energies of those modes are used as tuning parameters for the data-assimilation procedure, that will take as input typically (very) few point-wise time-resolved information. This technique will be applied in transitional flows such as the one around a squared-section cylinder, a benchmark case for oscillator flows, and a backward-facing-step, a typical noise-amplifier flow.We then consider a turbulent case corresponding to the flow around a squared-section cylinder at Re=22000, having both oscillator (periodic vortex-shedding) and noise-amplifier-like characteristics (represented by the Kelvin-Helmholtz structures). Classical mean-flow stability analysis is used to recover the the vortex-shedding mode and a resolvent technique, based on the linearized equations around the periodic component, is used to recover the dependency of the Kelvin-Helmholtz modes with the vortex-shedding
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Lakshmanan, Kris. "Quantitative computer image processing of color particle markers in flow visualization /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487265143146735.
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Pittard, Matthew T. "Large eddy simulation based turbulent flow-induced vibration of fully developed pipe flow /." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd295.pdf.
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Vosskuhle, Michel. "Particle collisions in turbulent flows." Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2013. http://tel.archives-ouvertes.fr/tel-00946618.
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Cette thèse est consacrée au mécanisme conduisant à des taux de collisions importants dans les suspensions turbulentes de particules inertielles. Le travail a été effectué en suivant numériquement des particules, par simulations directes des équations de Navier-Stokes, et également par étude de modèles simplifiés. Les applications de ce domaine sont nombreuses aussi bien dans un contexte industriel que naturel (astrophysique, géophysique). L'approximation des collisions fantômes (ACF), souvent utilisée pour déterminer les taux de collision numériquement, consiste à compter dans une simulation, le nombre de fois que la distance entre les centres de deux particules devient plus faible qu'une distance seuil. Plusieurs arguments théoriques suggéreraient que cette approximation conduit à une surestimation du taux de collision. Cette thèse fournit non seulement une estimation quantitative de cette surestimation, mais également une compréhension détaillée des mécanismes des erreurs faites par l'ACF. Nous trouvons qu'une paire de particules peut subir des collisions répétées avec une grande probabilité. Ceci est relié à l'observation que, dans un écoulement turbulent, certaines paires de particules peuvent rester proches pendant très longtemps. Une deuxième classe de résultats obtenus dans cette thèse a permis une compréhension quantitative des très forts taux de collisions souvent observés. Nous montrons que lorsque l'inertie des particules n'est pas très petite, l'effet " fronde/caustiques ", à savoir, l'éjection de particules par des tourbillons intenses, est responsable du taux de collision élevé. En comparaison, la concentration préférentielle de particules dans certaines régions de l'espace joue un rôle mineur.
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Sciacovelli, Luca. "Simulation numérique d'écoulements turbulents de gaz dense." Thesis, Paris, ENSAM, 2016. http://www.theses.fr/2016ENAM0061/document.
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Les écoulements turbulents de gaz denses, qui sont d’un grand intérêt pour un large éventail d'applications, sont le siège de phénomènes physiques encore peu connus et difficiles à étudier par des approches expérimentale. Dans ce travail, nous étudions pour la première fois l’influence des effets de gaz denses sur la structure de la turbulence compressible à l’aide de simulations numériques. Le fluide considéré est le PP11, un fluorocarbure lourd, dont le comportement thermodynamique a été représenté à l’aide de différentes lois d’état, afin de quantifier la sensibilité des solutions aux choix de modélisation. Nous avons considéré d’abord la décroissance d’une turbulence homogène isotrope compressible. Les fluctuations de température sont négligeables, alors que celles de la vitesse du son sont importantes à cause de leur forte dépendance de la densité. Le comportement particulier de la vitesse du son modifie de manière significative la structure de la turbulence, conduisant à la formation de shocklets de détente. L’analyse de la contribution des différentes structures à la dissipation d’énergie et à la génération d’enstrophie montre que, pour un gaz dense, les régions de forte dilatation jouent un rôle similaire à celles de forte compression, contrairement aux gaz parfaits, dans lesquels le comportement est fortement dissymétrique. Ensuite, nous avons mené des simulations numériques pour une configuration de canal plan en régime supersonique, pour plusieurs valeurs des nombres de Mach et de Reynolds. Les résultats confirment la validité de l’hypothèse de Morkovin. L’introduction d’une loi d’échelle semi-locale prenant en compte le variations de densité et viscosité, permet de comparer les profils des grandeurs turbulentes (contraintes de Reynolds, anisotropie, budgets d’énergie) avec ces observés en gaz parfait. Les variables thermodynamiques, quant à elles, présentent une évolution très différente pour un gaz parfait et pour un gaz dense, la chaleur spécifique élevée de ce dernier conduisant à un découplage des effets dynamiques et thermiques et à un comportement proche de celui d’un fluide incompressible avec des propriétés variablesDense gas turbulent flows, of great interest for a wide range of engineering applications, exhibit physical phenomena that are still poorly understood and difficult to reproduce experimentally. In this work, we study for the first time the influence of dense gas effects on the structure of compressible turbulence by means of numerical simulations. The fluid considered is PP11, a heavy fluorocarbon, whose thermodynamic behavior is described by means of different equations of state to quantify the sensitivity of solutions to modelling choices. First, we considered the decay of compressible homogeneous isotropic turbulence. Temperature fluctuations are found to be negligible, whereas those of the speed of sound are large because of the strong dependence on density. The peculiar behavior of the speed of sound significantly modifies the structure of the turbulence, leading to the occurrence of expansion shocklets. The analysis of the contribution of the different structures to energy dissipation and enstrophy generation shows that, for a dense gas, high expansion regions play a role similar to high compression ones, unlike perfect gases, in which the observed behaviour is highly asymmetric. Then, we carried out numerical simulations of a supersonic turbulent channel flow for several values of Mach and Reynolds numbers. The results confirm the validity of the Morkovin' hypothesis. The introduction of a semi-local scaling, taking into account density and viscosity variations across the channel, allow to compare the wall-normal profiles of turbulent quantities (Reynolds stresses, anisotropy, energy budgets) with those observed in ideal gases. Nevertheless, the thermodynamic variables exhibit a different evolution between perfect and dense gases, since the high specific heats of the latter lead to a decoupling of dynamic and thermal effects, and to a behavior close to that of variable property incompressible fluids
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Besnard, Stephane. "Performance and application of the Modular Acoustic Velocity Sensor (M.A.V.S.) current meter for laboratory measurements." Texas A&M University, 2004. http://hdl.handle.net/1969.1/1538.
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Every type of current meter is different and has its proper characteristics. Knowing the performance of a current meter is essential in order to use it properly either for field or laboratory measurements (such as in the Offshore Technology Research Center wave basin). A study of the MAVS (Modular Acoustic Velocity Sensor) in a wave basin is a first step essential for later deployment in real studies.
This thesis is based on data obtained from different series of laboratory measurements conducted in the OTRC wave basin. The objective of the first part of the study was to characterize the MAVS frequency response using benchmarks such as tow tests or wave tests. These benchmarks allowed us not only to characterize the sensor but also to eventually correct some of the measurement distortions due to flow blockage, vortex shedding, or vibrations of the mounting structure, for example.
After the preliminary study was done, we focused on the potential use of the MAVS in the OTRC wave basin. Indeed, in the case of a study of a scale model in the wave basin, the stresses applied to the model have to be accurately known. In the case of current-induced loads, this includes contributions from both the mean flow and the turbulence. Thus, after correcting the values measured by the MAVS, a mapping of the current jet was executed to determine its three-dimensional structure in the wave basin.
Knowing the structure of the current in the OTRC wave basin, it was then possible to define a domain in which the current can be considered uniform with a certain tolerable error. This domain of uniformity will allow us to validate the use of the OTRC wave basin to study large models such as FPSOs (Floating Production, Storage and Offloading Units).
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Lowe, Kevin Todd. "Design and application of a novel Laser-Doppler Velocimeter for turbulence structural measurements in turbulent boundary layers." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/29257.
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An advanced laser-Doppler velocimeter is designed to acquire fully-resolved turbulence structural measurements in high Reynolds number two- and three-dimensional turbulent boundary layers. The new instrument combines, for the first time, new techniques allowing for the direct measurement of particle acceleration and sub-measurement-volume-scale position resolution so that second-order 3D particle trajectories may be measured at high repetitions. Using these measurements, several terms in the Reynolds stress transport equations may be directly estimated, giving new data for modeling and understanding the processes leading to the transport of turbulence in boundary layer flows.
Due to the unique performance of the probe, many aspects of LDV instrumentation development were addressed. The LDV configuration was optimized for lowest uncertainties by considering the demanding applications of particle position and acceleration measurements. Low noise light detection and signal conditioning was specified for the three electronic channels. A high-throughput data acquisition system allows for exceptional burst rate acquisition. Signal detection and processing algorithms have been implemented which draw from previous techniques but also address distinctive problems with the current system. In short, the instrument was designed to advance the state-of-the-art in LDV systems.
Measurements presented include turbulence dissipation rate and fluctuating velocity-pressure gradient correlations that have been measured in 2D and 3D turbulent boundary layers using the unique capabilities of the CompLDV--many of these measurements are the first of their kind ever acquired in high Reynolds number turbulent flows. The flat-plate turbulent boundary layer is studied at several momentum thickness Reynolds numbers up to 7500 to examine Reynolds numbers effects on terms such as the velocity-pressure gradient correlation and the dissipation rate in the Reynolds transport equations. Measurements are also presented in a pressure-driven three-dimensional turbulent boundary layer created upstream from a wing-body junction. The current results complement the extensive data from previous studies and provide even richer depth of knowledge on the most-completely-documented 3D boundary layer flow in existence. Further measurements include the wakes of three circular-cylinder protuberances submerged in a constant pressure turbulent boundary layer.Ph. D.
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Beaumont, Ryan M. "Developing DNS Tools to Study Channel Flow Over Realistic Plaque Morphology." Fogler Library, University of Maine, 2007. http://www.library.umaine.edu/theses/pdf/BeaumontRM2007.pdf.
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Janyalertadun, Adun. "Computational fluid dynamic modelling of an inlet in a cross-flow." Thesis, University of Hertfordshire, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323460.
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Wu, Xuemei. "Monte-Carlo modeling of turbulent dispersion of small particles in channels." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/17389.
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Riley, Benjamin Matthew. "Magnetohydrodynamic lattice Boltzmann simulations of turbulence and rectangular jet flow." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1222.
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Guldsten, Jon Didriksen. "Influence on wind shear and turbulence in flow over obstacles." Thesis, Norwegian University of Science and Technology, Department of Energy and Process Engineering, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-10029.
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A wind tunnel study of speed-up effects above the very crest of a sharp-edged escarpment and a hill peak in a simulated atmospheric boundary layer has been carried out. It was desired to do a part-deep simulation of an atmospheric boundary that could be found above sea or coastal area exposed to the open sea. Because of the limited work section length was it used a modified roughness, barrier and mixing-device developed by Counihan to accelerate the boundary layer growth. The mean velocity, integral length scales, power spectrum and turbulence intensity in the simulated boundary layer were compared with full scale empirical data. It showed good agreement except for the turbulence intensity which was too low. Speed-up effects for the mean horizontal velocity and the longitudinal turbulence intensity above the very crest of an escarpment and a hill peak were investigated in the simulated atmospheric boundary layer. From the results it was observed that the speed-up effect gave a decrease in the turbulence intensity and a more uniform profile with height. A considerably increase of the horizontal mean velocity in the lowest part of the flow was also observed. Scaled-up data from the wind tunnel experiment were compared with estimations from the Norwegian standard and potential flow with varying degree of agreement.
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Zarraonandia, Gaizka. "Influence on wind shear and turbulence in flow over obstacles." Thesis, Norwegian University of Science and Technology, Department of Energy and Process Engineering, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-10165.
Full textAbstract:
A wind tunnel study of speed-up effects above the very crest of a sharp-edged escarpment and a hill peak in a simulated atmospheric boundary layer has been carried out. It was desired to do a part-depth simulation of an atmospheric boundary that could be found above sea or coastal area exposed to the open sea. Because of the limited work section length it was used a modified roughness, barrier and mixing-device method developed by Counihan to accelerate the boundary layer growth. The mean velocity, integral length scales, power spectrum and turbulence intensity in the simulated boundary layer were compared with full scale empirical data. It showed good agreement except for the turbulence intensity which was too low. Speed-up effects for the mean horizontal velocity and the longitudinal turbulence intensity above the very crest of an escarpment and a hill peak were investigated in the simulated atmospheric boundary layer. From the results it was observed that the speed-up effect gave a decrease in the turbulence intensity and a more uniform profile with height. In addition, it was observed a considerably increase of the horizontal mean velocity in the lowest part of the atmospheric boundary layer. Scaled-up data from the wind tunnel experiment were compared with estimations from the Norwegian standard and potential flow with varying degree of agreement.
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Zhang, Jian-Bo. "Turbulence measurements in shallow shear flow using video imaging method." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ30427.pdf.
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