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1
Cowan, Ian Robert. "Density-stratified turbulent boundary layers." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321001.
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Brandt, Rune. "Relaminarisation of turbulent boundary layers." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318288.
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Erm, Lincoln. "Low-Reynolds-number turbulent boundary layers /." Connect to thesis, 1988. http://eprints.unimelb.edu.au/archive/00000226.
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Barreto-Acobe, Clary Denisse 1976. "Turbulent wave-current boundary layers revisited." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/84239.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2001.<br>Includes bibliographical references (leaves 91-94).<br>by Clary Denisse Barreto-Acobe.<br>S.M.
5
Tahouri, Bahman. "Semi-cylindrical structures in turbulent boundary layers." Thesis, University of Surrey, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357036.
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Ahn, Seungki. "Some unsteady features of turbulent boundary layers." Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/53090.
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For steady free-stream, zero and favorable pressure gradient turbulent
boundary layers, the unsteadiness in the form of turbulent fluetuations was
investigated. Phase ensemble-averaged flow characteristics of a large amplitude
periodic unsteady turbulent boundary layer was also investigated at a redueed
frequency k = 0.61 based on the length of the eonverging and diverging test
section with amplitude to mean velocity ratio of 0.8.
ln steady flow cases, both zero and favorable pressure gradient flows show
good two—dimensional flow characteristics and mean flow characteristics are
compared with other researchers’ data. Measured power spectral data show good
agreement with those of Klebanoff, Ueda and Hinze, Perry, Lim and Henbest for
the zero pressure gradient flows and Jones and Launder for the favorable
pressure gradient flow. The power spectral data measured in the turbulent wall
region of the zero pressure gradient flow closely follow the model equation
proposed by Perry, Lim and Henbest. Convective wave speed also show good
agreement with those of Favre, Gaviglio and Dumas and Sternberg within the
experimental uncertainties. ln the inner region of the boundary layer where
y+ < 40, convective wave speed is higher than local mean velocity at all eddy
scales as observed by Kline, Reynolds, Schraub and Runstadler.
In the unsteady flow case, in the absence of flow reversal, the flow behaves
in a quasi-steady manner and can be described by the steady flow structure as in
the case of moderate amplitude flows. The Ludwieg·Tillmann skin friction
equation and the Perry-Schofield universal velocity defect law hold at these
phases. Except the laminariscent velocity profile observed during the acceleration
phases, the large amplitude unsteady flow shows basically the same flow
characteristics as the moderate amplitude flows.<br>Master of Science
7
Li, Qiang. "Simulations of turbulent boundary layers with heat transfer." Licentiate thesis, Stockholm : Skolan för teknikvetenskap, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11320.
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Ahn, B. K. "Modelling unsteady wall pressures beneath turbulent boundary layers." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595397.
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The objective is to estimate the surface pressure distributions and corresponding spectra induced by fully developed hairpin vortices inclined at an angle of 45 degree to the wall in turbulent boundary layers. On the assumption that fully developed hairpin vortices are governed by inviscid dynamics, we obtain an exact formulation for the stagnation pressure, in terms of a Green function integral along the vortex lines. We then evaluate the surface static pressure by subtracting the dynamic pressure from the results of this formulation applied to our vortex geometry. On the basis of the attached eddy model, which implies that the form of the wave number spectrum can be deduced from the properties of a single eddy, we develop the expressions needed for the surface pressure spectra in terms of eddy number-density. This approach draws on flow visualization evidence, which indicates that the number of eddies observed in both streamwise and spanwise directions of the flow is inversely proportional to their size. The overall wavenumber spectrum consists of contributions from eddies of all sizes, weighted by the number-density. From a parameter study we investigate the influence of varying the largest and smallest eddy scales for different eddy aspect ratios. We then validate our model against existing descriptions and measurements of turbulent boundary layer pressures. We examine the predicted wave number spectra and compare them with those of existing empirical models, available direct numerical simulation and also with the results of flight-test measurements. The present model clearly predicts a theoretically-expected characteristic of the wavenumber spectrum (the -1 slope), whereas this is absent from the empirical models. This discrepancy apart, good quantitative agreement is achieved, particularly for the spanwise (cross-flow) spectrum. The agreement is best for the novel formulation for off-axis correlations proposed by Smol'yakov and Tkachenko (1991), rather than the traditional form (e.g. Corcos). The comparison with flight-test data is made via predicted and measured spatial correlations, and again shows good agreement. The present hairpin vortex model shows that it is capable of predicting the properties of the wall pressure field, and is therefore a promising candidate for use in exploring features less readily obtainable by other methods, e.g. off-axis correlations.
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Gough, Tim. "Low Reynolds number turbulent boundary layers and wakes." Thesis, University of Surrey, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360949.
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Tsuji, Yoshiyuki. "Peak position of dissipation spectrum in turbulent boundary layers." The American Physical Society, 1999. http://hdl.handle.net/2237/7145.
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Ekoto, Isaac Wesley. "Supersonic turbulent boundary layers with periodic mechanical non-equilibrium." Texas A&M University, 2006. http://hdl.handle.net/1969.1/4709.
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Previous studies have shown that favorable pressure gradients reduce the
turbulence levels and length scales in supersonic flow. Wall roughness has been shown to
reduce the large-scales in wall bounded flow. Based on these previous observations new
questions have been raised. The fundamental questions this dissertation addressed are: (1)
What are the effects of wall topology with sharp versus blunt leading edges? and (2) Is it
possible that a further reduction of turbulent scales can occur if surface roughness and
favorable pressure gradients are combined? To answer these questions and to enhance the
current experimental database, an experimental analysis was performed to provide high
fidelity documentation of the mean and turbulent flow properties along with surface and
flow visualizations of a high-speed ( 2.86 M = ), high Reynolds number (Re 60,000 q û )
supersonic turbulent boundary layer distorted by curvature-induced favorable pressure
gradients and large-scale ( 300 s k + û ) uniform surface roughness. Nine models were tested
at three separate locations. Three pressure gradient models strengths (a nominally zero, a
weak, and a strong favorable pressure gradient) and three roughness topologies
(aerodynamically smooth, square, and diamond shaped roughness elements) were used.
Highly resolved planar measurements of mean and fluctuating velocity components were
accomplished using particle image velocimetry. Stagnation pressure profiles were acquired with a traversing Pitot probe. Surface pressure distributions were characterized
using pressure sensitive paint. Finally flow visualization was accomplished using
schlieren photographs.
Roughness topology had a significant effect on the boundary layer mean and
turbulent properties due to shock boundary layer interactions. Favorable pressure
gradients had the expected stabilizing effect on turbulent properties, but the
improvements were less significant for models with surface roughness near the wall due
to increased tendency towards flow separation. It was documented that proper roughness
selection coupled with a sufficiently strong favorable pressure gradient produced regions
of âÂÂnegativeâ production in the transport of turbulent stress. This led to localized areas of
significant turbulence stress reduction. With proper roughness selection and sufficient
favorable pressure gradient strength, it is believed that localized relaminarization of the
boundary layer is possible.
12
Babinsky, Holger. "A study of roughness in turbulent hypersonic boundary-layers." Thesis, Cranfield University, 1993. http://dspace.lib.cranfield.ac.uk/handle/1826/7586.
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The influence of large scale regular roughness on a Mach 5 turbulent boundary
layer and a compression corner was investigated on axisymmetric wind tunnel
models. Three types of roughness were examined; a series of square cavities at
two different sizes and a 45 degree sawtooth. Typical sizes ranged from 50% to
100% of an undisturbed boundary layer thickness. The roughness was limited to
a short region followed by a smooth surface. Compression corners were formed
by 15° and 20° flares located downstream of the roughness. The flow in the wind
tunnel was investigated in detail to obtain knowledge on operating conditions and
flow quality. Liquid crystal thermography was developed for routine use in
hypersonic blow-down wind tunnels with superior spatial resolution and
experimental uncertainties in the range of traditional techniques.
The effect on flow parameters downstream of the last roughness element were 7,
found to differ significantly for the different quantities. Velocity profiles were found i,
to be less full and skin friction was found to be reduced for all streamwise "~
distances. Surface heat transfer was increased in a short region limited to 1.5
boundary layer thicknesses behind the roughness whereas surface pressure was
not affected. Sawtooth shaped roughness was found to cause a stronger j
disturbance than square cavities of twice the size. Little influence of the
roughness was noted on the flow over the compression corner. The flow over the
20° compression corner showed an increase in upstream influence for the
sawtooth shaped roughness as well as the larger cavities. Surface pressure
measurements did not indicate a separation in any case. Heat transfer
measurements revealed a peak located approximately 0.25 boundary layer
thicknesses behind the corner. No such feature was found in the surface
pressure distributions. It is suggested that a small scale separation is located very
close to the corner causing the peak in heat transfer at reattachment without any
effect on surface pressures. The existence of such a separation has been
confirmed by surface flow visualisations for both flares.
13
Yuan, Jing Ph D. Massachusetts Institute of Technology. "Experimental and theoretical study of turbulent oscillatory boundary layers." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/85821.
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Thesis: Ph. D. in Environmental Fluid Mechanics, Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2013.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 241-244).<br>Sediment transport is of crucial importance to engineering projects in coastal regions, so it is of primary interest in coastal engineering. The driving forces for sediment transport are mostly determined by the hydrodynamics of oscillatory turbulent bottom boundary layers, which is still not well understood. Therefore, the goal of this thesis is to improve the present experimental and theoretical understandings on this subject. A high-quality experimental study including a large number of tests which correspond to full-scale coastal boundary layer flows is performed using a state-of-the-art oscillating water tunnel (OWT) for flow generations and a Particle Image Velocimetry system for velocity measurements. The experimental results suggest that the logarithmic profile can accurately represent the boundary layer flows in the very near-bottom region, so the log-profile fitting analysis can give highly accurate determinations of the hydrodynamic roughness, the theoretical bottom location and the bottom shear stress. The current velocity profiles in the presence of sinusoidal waves indicate a two-log-profile structure suggested by the widely-used Grant-Madsen model. However, for weak currents in the presence of nonlinear waves, the two-log-profile structure is contaminated or even totally obliterated by the boundary layer streaming which is related with the temporal variation of the turbulent eddy viscosity. This, together with some other experimental evidence, motivates the development of a new theoretical model which adopts a rigorous way to account for a time-varying turbulent eddy viscosity. The model accurately predicts the mean and leading Fourier components of the velocity and the bottom shear stress for various flow conditions. Most importantly, the boundary layer streaming related to the time-varying turbulent eddy viscosity is reasonably predicted, which leads to successful predictions of the mean velocity embedded in nonlinear-wave tests and the current velocity profiles in the presence of either sinusoidal or nonlinear waves. The predictions reveal significant differences between boundary layer flows in OWTs and in the coastal environment, which must be considered when interpreting OWT results for sediment transport.<br>by Jing Yuan.<br>Ph. D. in Environmental Fluid Mechanics
14
DiGregorio, Nicholas J. "Characteristics of Turbulent Boundary Layers along a Hypersonic Vehicle." Thesis, State University of New York at Buffalo, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10822170.
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<p> The flight conditions of a hypersonic vehicle on an ascent trajectory are computed and Reynolds-averaged Navier-Stokes (RANS) simulations of the turbulent boundary layers are performed across a Mach number range of 0.3 up to 16 using the computational fluid dynamics (CFD) software, VULCAN. The boundary conditions and leading edge geometry are varied from the simple case of adiabatic and sharp to cooled and blunted to reveal the physics of how these effects impact the results of flat plate boundary layer methods as applied to practical aerospace systems. The law of the wall, the Van Driest transformation, and a shear stress preserving transformation's ability to collapse boundary layer velocity profiles under the conditions of variable wall boundary condition and leading edge geometry is explored. </p><p> Boundary layer related quantities examined include the boundary layer thickness, local skin friction coefficient, displacement thickness, momentum thickness, heat flux, and integrated loads. It is found that cooling the surface serves to increase the density of the boundary layer, making it thinner. This thinning of the boundary layer thickness increases the velocity gradients, thus increasing the shear stresses and the local skin friction coefficient. The effects on turbulent boundary layers of blunting the leading edge are explained by the difference in properties, particularly viscosity, caused by a detached bow shock instead of a Mach wave that comes off of a sharp nose plate. Heat flux into a vehicle is found to be insignificant at low speeds, but increases drastically as the Mach number rises into the supersonic and hypersonic regimes. It is observed that the integrated skin friction coefficient decreases as Mach number increases and the leading edge becomes blunted, however, it increases as more cooling is applied at the boundary. The integrated heat flux computed from a sharp leading edge geometry is greater compared to a blunted leading edge due to greater temperature gradients in the sharp nose case relative to the blunt nose case. </p><p> The shear stress preserving transformation, derived with the inclusion of a stress balance condition, is found to produce a better collapse of the velocity profile data than the Van Driest transformation and the incompressible law of the wall regardless of Mach number, boundary condition or leading edge geometry. The normalized untransformed velocity gradients are compared to the velocity gradients resulting from the Van Driest and shear stress preserving tranformation. It is shown that the velocity gradients from the shear stress preserving match the normalized untransformed velocity gradients more closely than the Van Driest velocity gradients do. The advantages, disadvantages, and limitations of each transformation are discussed.</p><p>
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Kuhl, David Derieg. "Near Wall Investigation of Three Dimensional Turbulent Boundary Layers." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/34676.
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This report documents the experimental study for four different three-dimensional turbulent flows. The investigation focuses on near wall measurements in these flows. Several experimental techniques are used in the studies; however, the bulk of the investigation focuses on a three-orthogonal-velocity-component fiber-optic laser Doppler anemometer (3D-LDA) system. The control volume of the 3D-LDA is on the order of 50 micro-meter in size, or a y<sup>+</sup> distance of around 2.3 units (using average values of U<sub>τ</sub> and ν from the experiment). An auxiliary small boundary layer wind tunnel (auxiliary tunnel) and a low speed linear compressor cascade wind tunnel (cascade tunnel) are utilized in this study. One of four flow experiments is done in the auxiliary tunnel the other three are in the cascade tunnel. The first three-dimensional turbulent flow is a vortical flow created by two half-delta wing vortex generators. Near wall secondary flow features are found. The second flow is an investigation of the first quarter chord tip gap flow in the cascade tunnel. Strong three-dimensional phenomena are found. The third flow investigated is the inflow to the compressor cascade with the moving wall. The experiment records shear layer interaction between the upstream flow and moving wall. Finally the fourth flow investigated is the inflow to the compressor cascade with the moving wall with half-delta wing vortex generators attached. Phase-averaged data reveal asymmetrical vortex structures just downstream of the vortex generators. This is the first time any near wall data has been taken on any of these flows.<br>Master of Science
16
Bobke, Alexandra. "Simulations of turbulent boundary layers with suction and pressure gradients." Licentiate thesis, KTH, Linné Flow Center, FLOW, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-185275.
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The focus of the present licentiate thesis is on the effect of suction and pressure gradients on turbulent boundary-layer flows, which are investigated separately through performing numerical simulations.The first part aims at assessing history and development effects on adverse pressure-gradient (APG) turbulent boundary layers (TBL). A suitable set-up was developed to study near-equilibrium conditions for a boundary layer developingon a flat plate by setting the free-stream velocity at the top of the domain following a power law. The computational box size and the correct definition of the top-boundary condition were systematically tested. Well-resolved large-eddy simulations were performed to keep computational costs low. By varying the free-stream velocity distribution parameters, e.g. power-law exponent and virtual origin, pressure gradients of different strength and development were obtained. The magnitude of the pressure gradient is quantified in terms of the Clauser pressure-gradient parameter β. The effect of the APG is closely related to its streamwise development, hence, TBLs with non-constant and constant β were investigated. The effect was manifested in the mean flow through a much more pronounced wake region and in the Reynolds stresses through the existence of an outer peak. The terms of the turbulent kinetic energy budgets indicate the influence of the APG on the distribution of the transfer mechanism across the boundary layer. Stronger and more energetic structures were identified in boundary layers with relatively stronger pressure gradients in their development history. Due to the difficulty of determining the boundary-layer thickness in flows with strong pressure gradients or over a curvedsurface, a new method based on the diagnostic-plot concept was introduced to obtain a robust estimation of the edge of a turbulent boundary layer. In the second part, large-eddy simulations were performed on temporally developing turbulent asymptotic suction boundary layers (TASBLs). Findings from previous studies about the effect of suction could be confirmed, e.g. the reduction of the fluctuation levels and Reynolds shear stresses. Furthermore, the importance of the size of the computational domain and the time development were investigated. Both parameters were found to have a large impact on the results even on low-order statistics. While the mean velocity profile collapses in the inner layer irrespective of box size and development time, a wake region occurs for too small box sizes or early development time and vanishes once sufficiently large domains and/or integration times are chosen. The asymptotic state is charactersized by surprisingly thick boundary layers even for moderateReynolds numbers Re (based on free-stream velocity and laminar displacement thickness); for instance, Re = 333 gives rise to a friction Reynolds number Reτ = 2000. Similarly, the flow gives rise to very large structures in the outer region. These findings have important ramifications for experiments, since very large facilities are required to reach the asymptotic state even for low Reynolds numbers.<br><p>QC 20160418</p>
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Mukha, Timofey. "Inflow generation for scale-resolving simulations of turbulent boundary layers." Licentiate thesis, Uppsala universitet, Avdelningen för beräkningsvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-302808.
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Generating inflow fields for scale-resolving simulations of turbulent flow is crucial for a wide range of applications and is an active area of research. In this thesis, a method for inflow generation employing a precursor turbulent channel flow simulation is proposed. A procedure for determining the parameters of the precursor simulation based on the properties of the inflow is given. To evaluate the performance of the method, results from a simulation of a flat-plate zero-pressure-gradient turbulent boundary layer are analysed. The adaption length is quantified in terms of the development of integral quantities and the statistical moments of the velocity field. The performance is also compared with that of a state-of-the-art rescaling method for the generation of inflow data. It is shown that both approaches result in adaption lengths of comparable sizes, which makes the proposed method an attractive alternative due to its conceptual simplicity and robustness. As part of the work on inflow generation, a Python package, eddylicious, was developed. The purpose of the package is to be a framework within which various generation methods can be implemented. The package is available online under an open-source license. An overview of the architecture and currently implemented functionality of the package is given in this thesis. Furthermore, the results of a preparatory study on large-eddy simulation of wall-bounded turbulent flows are discussed. Fully-developed turbulent channel flow is used as a model problem, and the general-purpose computational fluid dynamics solver OpenFOAM is employed. The accuracy of the results with respect to the resolution of the computational mesh is analysed. Several modelling approaches for the subgrid scale stresses are considered.
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Arnette, Stephen Andrew. "The effects of expansion regions on supersonic turbulent boundary layers /." The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487865929454911.
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Orsi, Filho Edgar. "An Experimental Study of Turbulent Boundary Layers Subjected to High Free-stream Turbulence Effects." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/36460.
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The work presented in this thesis was on nominally two-dimensional turbulent boundary layers at zero pressure gradient subjected to high free-stream turbulent intensities of up to 7.9% in preparations for high free-stream turbulence studies on three-dimensional boundary layers, which will be done in the future in the Aerospace and Ocean Engineering Boundary Layer Wind Tunnel at Virginia Tech. The two-dimensional turbulent flow that will impinge three-dimensional bodies needed to be characterized, before the three-dimensional studies can be made. An active turbulence generator designed to create high free-stream turbulence intensities in the wind tunnel was tested and modified in order to obtain the lowest possible mean flow non-uniformities. A seven-hole pressure probe was used to obtain planes of mean velocity measurements. A three-component state of the art laser-Doppler velocimeter (LDV) was used to obtain mean and fluctuating velocities. Previous high free-stream turbulence studies have been reviewed and are discussed, and some of the previously published data of other authors have been corrected. Based on the measurements obtained with the LDV, it was also determined that the semi-log law of the wall is valid for high free-stream turbulence cases, but with different constants than the ones proposed by Coles, where the constants for the high free-stream cases may be dependent on the turbulence intensity. For the first time, the skin friction coefficient (Cf) was deduced from the viscous sublayer. The difference between the U_tau obtained in the viscous sublayer mean velocity profile and the U_tau obtained in the semi-log layer was 1.5%. The skin friction coefficient was determined to increase by 10.5% when the two-dimensional turbulent boundary layer was subjected to high free-stream turbulence effects. Spectral data obtained with the LDV, were compared to the von Kármán model spectrum and to the Pope's model spectrum, where the von Kármán spectrum was proven to fit the spectral data slightly better than the Pope's spectrum. Finally, the Hancock-Bradshaw-Blair parameter obtained for this experiment agreed very well with previously published data.<br>Master of Science
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Wang, Kan. "Computational investigation of aero-optical distortions by turbulent boundary layers and separated shear layers." Thesis, University of Notre Dame, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3578995.
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<p> Aero-optical distortions are detrimental to airborne optical systems. To study distortion mechanisms, compressible large-eddy simulations are performed for a Mach 0.5 turbulent boundary layer and a separated shear layer over a cylindrical turret with and without passive control in the upstream boundary layer. Optical analysis is carried out using ray tracing based on the computed density field and Gladstone-Dale relation.</p><p> In the flat-plate boundary layer, the effects of aperture size, Reynolds number, small-scale turbulence, different flow regions and beam elevation angle are examined, and the underlying flow physics is analyzed. Three momemtum-thickness Reynolds numbers, <i>Re</i><sub>&thetas;</sub> = 875, 1770 and 3550, are considered. It is found that the level of optical distortions decreases with increasing Reynolds number within the Reynolds number range considered. The contributions from the viscous sublayer and buffer layer are small, while the wake region plays a dominant role followed by the logarithmic layer. By low-pass filtering the fluctuating density field, it is shown that small-scale turbulence is optically inactive. Consistent with previous experimental findings, the distortion magnitude is dependent on the propagation direction due to anisotropy of the boundary-layer vortical structures. Density correlations and length scales are analyzed to understand the elevation-angle dependence and its relation to turbulence structures. The applicability of Sutton's linking equation to boundary-layer flows is examined, and excellent agreement between linking equation predictions and directly integrated distortions is obtained when the density length scale is appropriately defined.</p><p> The second case studied involves a separated shear layer over a cylindrical turret with a flat window, with inflow from a flat-plate boundary layer with and without passive control devices. The flow and optical results show reasonable agreement with experimental data for the baseline case without control. Aperture size effect, frequency spectra of OPD and two-point spatial correlations of OPD are investigated. The similarities and differences of distortion characteristics compared to those induced by turbulent boundary layers are discussed. The distortions by a separated shear layer are much larger in magnitude and spatially less homogeneous than those induced by an attached boundary layer. It is found that pressure fluctuations are significant and play a dominant role in inducing density fluctuations and associated optical distortions in a separated shear layer, in contrast to the dominant role of temperature fluctuations in a turbulent boundary layer. When passive control is applied using a row of thin and tall pins in the upstream boundary layer, the numerical results confirm key experimental findings. The flow above the optical window is characterized by two distinct shear layers, whose combined effect leads to a significant reduction of density fluctuation magnitude in the main shear layer and associated optical distortions compared to the uncontrolled flow with a single strong shear layer.</p>
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Tachie, Mark Francis. "Open channel turbulent boundary layers and wall jets on rough surfaces." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ63927.pdf.
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Rahman, Shikha. "Effect of bed roughness on scalar mixing in turbulent boundary layers." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/32794.
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Bird, James William. "Controlling turbulent boundary layers through the actuation of a compliant structure." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/55878.
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The control of turbulent boundary layers through spanwise wall forcing has been the subject of extensive numerical and experimental investigation in recent years. It has been shown that the benefits of drag reduction and potential power saving are enhanced when the forcing takes the form of a streamwise travelling wave of spanwise velocity. When this wave has a certain non-dimensional frequency and wavenumber, large turbulent skin-friction drag reductions of almost 50% and potential net power savings of 38% can be achieved. While there are numerous direct numerical simulations (DNS) showing these trends, an experimental validation was lacking for boundary layer flows. The work presented details the design and manufacture of an active surface, capable of discretising these complex waveforms to bring about turbulent flow-control in a wind tunnel experiment. Through the optimal design of a compliant structure, based on the Kagome lattice geometry, an adaptive framework was developed which is capable of discretising waveforms through controlled local deformation. By combining this compliant structure with a pre-tensioned membrane, an active surface is produced. The surface, 3 m in length, is then driven pneumatically, producing surface travelling waves of variable wavenumber and phase velocity. Photogrammetric and vibrometer measurements of the static and dynamic performance of actuated surface are presented. Constant temperature anemometer measurements of the boundary layer were taken with and without the active surface applying forcing. A linear interpolation of the viscous sub-layer was performed to assess changes in wall shear-stress. For certain forcing parameters, a drag reduction of 20% was measured.
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Rodriguez, Lopez Eduardo. "Effect of strong disturbances on the evolution of turbulent boundary layers." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/51418.
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This thesis describes an experimental investigation into the evolution of artificially generated high Reynolds number turbulent boundary layers (TBL). Due to its large importance on TBL scaling, skin friction has to be accurately determined. With this purpose, a robust post-processing method is developed to extract the mean skin friction and the wall-probe relative position from the mean velocity profile with uncertainties better than 1% and 0.5 wall units respectively. For disrupted TBLs, it is shown that, after a certain disturbance, TBLs evolve towards a canonical state after an adaptation region whose turbulent properties and length are strongly dependent on the trips' geometry. Two distinct mechanisms (so called wall-driven and wake-driven) are identified and associated with shorter and longer adaptation regions respectively. The latter is generated by disruptions exhibiting strong flow recirculation which enhances the influence of the obstacle's wake on the near-wall region and compromises the TBL properties in the adaptation region. Contrastingly, trips generating a wall-driven mechanism prevent this interaction from happening thus enabling a distinction between the trips' wakes and the near-wall region. Particle image velocimetry and low-order modelling of the flow in the close vicinity of the obstacles enable us to establish a three-way link between the main geometrical features of the trips, the length of the adaptation region and its turbulent properties. Low-porosity wall-mounted single- and multi-scale fences are designed and tested to control the degree of interaction between their wake and the near-wall region. Turbulent properties in the near-wall region are shown to scale with the local thickness of that internal layer rather than with the thickness of the whole fence's wake. Further, an aero-acoustic characterization of the flow is conducted showing the spatial distribution and the velocity scalability of the noise sources. Finally, some topics for further work are proposed.
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Schmidt, Martin Arnold. "Microsensors for the measurement of shear forces in turbulent boundary layers." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14781.
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Jocksch, Andreas. "Direct numerical simulation of turbulent spots in high-speed boundary layers." Konstanz Hartung-Gorre, 2008. http://d-nb.info/996782192/04.
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Morita, Yuki. "Robust optimisation of the pressure-gradient distribution in turbulent boundary layers." Thesis, KTH, Mekanik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-272009.
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In order to better characterise pressure-gradient turbulent boundary layers (TBLs), and to advance the theory of these flows, typically canonical conditions are required. This is achieved by keeping the Clauser pressure-gradient parameter, β, constant along the streamwise direction, see for instance Mellor and Gibson [9] and Bobke et al. [1] It is, however, very challenging to obtain the correct boundary conditions when performing numerical simulations or wind-tunnel experiments so that a give mean pressure gradient is kept constant along the edge of a turbulent boundary layer. This study tackles this issue through numerically optimising the shape of the upper boundary of a 2D channel flow to obtain a target constant-β distribution at the TBL over the bottom wall. The shape of the upper boundary of the channel is parameterised and the parameters are optimised through Bayesian optimisation based on Gaussian process regressiong (GPR). To simulate the turbulent flow within the channel at a low computational cost, steady RANS (Reynolds-Averaged Navier-Stokes) simulations are conducted, which show a good agreement with DNS (Direct Numerical Simulation) and LES (Large-Eddy Simulation) benchmark data. The simulations are performed using the open-source finite-volume-based software OpenFoam. Through the optimisation process, constant-β distributions are achieved after few iterations for several target values of β, corrensponding to ZPG (zero-pressure-gradient) and APG (adverse-pressure-gradient) TBLs. The results of constant-β distributions show very good agreement with reference data. The impact of parameterisation of the upper wall on the performance of the optimisation and the accuracy of the results is also studied. This study can be a very powerful tool to set constant-β distributions in experiments.
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Hipp, Hans Christoph 1959. "Numerical investigation of mode interaction in free shear layers." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276871.
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Numerical simulations of incompressible, two-dimensional, monochromatically and bichromatically forced laminar free shear layers are performed on the basis of a vorticity-velocity formulation of the complete Navier-Stokes equations employing central finite differences. Spatially periodic shear layers developing in time (temporal model) are compared with shear layers developing in the stream-wise direction (spatial model). The regimes of linear growth and saturation of the fundamental are quantitatively scrutinized, the saturation of the subharmonic and vortex merging are investigated, and the effects of a forcing phase-shift between fundamental and subharmonic. For the spatial model the appearance of an unforced subharmonic was also examined. It was found that contrary to temporal shear layers a significant control of vortex merging by means of a forcing phase-shift and vortex shredding are not possible in spatial shear layers due to strong dispersion.
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Khapko, Taras. "Edge states and transition to turbulence in boundary layers." Doctoral thesis, KTH, Stabilitet, Transition, Kontroll, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-186038.
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The focus of this thesis is the numerical study of subcritical transition to turbulence in boundary-layer flows. For the most part, boundary layers with uniform suction are considered. Constant homogeneous suction counteracts the spatial growth of the boundary layer, rendering the flow parallel. This enables research approaches which are not feasible in the context of spatially developing flows. In the first part, the laminar–turbulent separatrix of the asymptotic suction boundary layer (ASBL) is investigated numerically by means of an edge-tracking algorithm. The obtained edge states experience recurrent dynamics, going through calm and bursting phases. The self-sustaining mechanism bears many similarities with the classical regeneration cycle of near-wall turbulence. The recurrent simple structure active during calm phases is compared to the nucleation of turbulence events in bypass transition originating from delocalised initial conditions. The implications on the understanding of the bypass-transition process and the edge state's role are discussed. Based on this understanding, a model is constructed which predicts the position of the nucleation of turbulent spots during free-stream turbulence induced transition in spatially developing boundary-layer flow. This model is used together with a probabilistic cellular automaton (PCA), which captures the spatial spreading of the spots, correctly reproducing the main statistical characteristics of the transition process. The last part of the thesis is concerned with the spatio-temporal aspects of turbulent ASBL in extended numerical domains near the onset of sustained turbulence. The different behaviour observed in ASBL, i.e. absence of sustained laminar–turbulent patterns, which have been reported in other wall-bounded flows, is associated with different character of the large-scale flow. In addition, an accurate quantitative estimate for the lowest Reynolds number with sustained turbulence is obtained<br><p>QC 20160429</p>
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Miller, Ronald J. "A Study of Passive Scalar Mixing in Turbulent Boundary Layers using Multipoint Correlators." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7574.
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This study analyzes a turbulent passive scalar field using two-point and three-point correlations of the fluctuating scalar field. Multipoint correlation functions are investigated because they retain scaling property information and simultaneously probe the concentration field for the spatial structure of the scalar filaments. Thus, multipoint correlation functions provide unique information about the spatial properties of the concentration filaments. The concentration field is created by the iso-kinetic release of a high Schmidt number dye into a fully developed turbulent boundary layer of an open channel flow. The concentration fields were previously measured using the planar laser-induced fluorescence technique.
The two-point correlations of the fluctuating scalar field indicate that as the scalar field evolves downstream, the anisotropic influence of the tracer injection method diminishes, and the scalar field becomes dominated by the mean velocity shear. As the scalar filaments align with the mean velocity gradient, the elliptical shape associated with the contours of the correlation function tilts in the direction of the mean velocity gradient. As a result, the two-point correlation contours of the concentration fluctuations indicate that anisotropic conditions (i.e. the tilted, asymmetric, elliptical shape) develop as a consequence of the mean velocity shear.
Three-point correlations of the fluctuating scalar field are calculated based on configuration geometries defined by previous researchers. The first configuration follows Mydlarski and Warhaft (1998), which employs two cold-wire measurements and Taylor's frozen turbulence hypothesis. The three-point correlation contours of the concentration fluctuations associated with the cold-wire measurements exhibit a symmetric characteristic V-shape. Similar symmetric properties are observed in the current study. The second set of configurations follows on recent theoretical predictions, which indicate that the three-point correlation of the fluctuating scalar field is dependent on the size, shape, and orientation of the triangle created by the three points. The current study analyzes two geometric configurations (isosceles and collinear). The geometric configurations are defined to ensure that the influence of the shape remains constant as the configuration is rotated, translated, and dilated. Additionally, the scaling exponent in the inertial-convective regime is calculated to determine the dependence of the correlation function on the size of the triangle pattern.
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Kim, Kyoungjin. "Computation of wake-passing effects on turbine blade boundary layers /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Dasi, Lakshmi P. "The small-scale structure of passive scalar mixing in turbulent boundary layers." Diss., Available online, Georgia Institute of Technology, 2004, 2004. http://etd.gatech.edu/theses/available/etd-08132004-065041/.
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Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006.<br>Cvitanovic, Predrag, Committee Member ; Roberts, Phillip, Committee Member ; Sturm, Terry, Committee Member ; Webster, Donald, Committee Chair ; Yeung, Pui-Kuen, Committee Member.
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TSUJI, Y., J. H. M. FRANSSON, P. H. ALFREDSSON, and A. V. JOHANSSON. "Pressure statistics and their scaling in high-Reynolds-number turbulent boundary layers." Cambridge University Press, 2007. http://hdl.handle.net/2237/10508.
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Örlü, Ramis. "Experimental studies in jet flows and zero pressure-gradient turbulent boundary layers". Doctoral thesis, KTH, Mekanik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10448.
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This thesis deals with the description and development of two classical turbulent shear flows, namely free jet and flat plate turbulent boundary layer flows. In both cases new experimental data has been obtained and in the latter case comparisons are also made with data obtained from data bases, both of experimental and numerical origin. The jet flow studies comprise three parts, made in three different experimental facilities, each dealing with a specific aspect of jet flows. The first part is devoted to the effect of swirl on the mixing characteristics of a passive scalar in the near-field region of a moderately swirling jet. Instantaneous streamwise and azimuthal velocity components as well as the temperature were simultaneously accessed by means of combined X-wire and cold-wire anemometry. The results indicate a modification of the turbulence structures to that effect that the swirling jet spreads, mixes and evolves faster compared to its non-swirling counterpart. The high correlation between streamwise velocity and temperature fluctuations as well as the streamwise passive scalar flux are even more enhanced due to the addition of swirl, which in turn shortens the distance and hence time needed to mix the jet with the ambient air. The second jet flow part was set out to test the hypothesis put forward by Talamelli & Gavarini (Flow, Turbul. & Combust. 76), who proposed that the wake behind a separation wall between two streams of a coaxial jet creates the condition for an absolute instability. The experiments confirm the hypothesis and show that the instability, by means of the induced vortex shedding, provides a continuous forcing mechanism for the control of the flow field. The potential of this passive mechanism as an easy, effective and practical way to control the near-field of interacting shear layers as well as its effect towards increased turbulence activity has been shown. The third part of the jet flow studies deals with the hypothesis that so called oblique transition may play a role in the breakdown to turbulence for an axisymmetric jet.For wall bounded flows oblique transition gives rise to steady streamwise streaks that break down to turbulence, as for instance documented by Elofsson & Alfredsson (J. Fluid Mech. 358). The scenario of oblique transition has so far not been considered for jet flows and the aim was to study the effect of two oblique modes on the transition scenario as well as on the flow dynamics. For certain frequencies the turbulence intensity was surprisingly found to be reduced, however it was not possible to detect the presence of streamwise streaks. This aspect must be furher investigated in the future in order to understand the connection between the turbulence reduction and the azimuthal forcing. The boundary layer part of the thesis is also threefold, and uses both new data as well as data from various data bases to investigate the effect of certain limitations of hot-wire measurements near the wall on the mean velocity but also on the fluctuating streamwise velocity component. In the first part a new set of experimental data from a zero pressure-gradient turbulent boundary layer, supplemented by direct and independent skin friction measurements, are presented. The Reynolds number range of the data is between 2300 and 18700 when based on the free stream velocity and the momentum loss thickness. Data both for the mean and fluctuating streamwise velocity component are presented. The data are validated against the composite profile by Chauhan et al. (Fluid Dyn. Res. 41) and are found to fulfil recently established equilibrium criteria. The problem of accurately locating the wall position of a hot-wire probe and the errors this can result in is thoroughly discussed in part 2 of the boundary layer study. It is shown that the expanded law of the wall to forth and fifth order with calibration constants determined from recent high Reynolds number DNS can be used to fix the wall position to an accuracy of 0.1 and 0.25 l_ * (l_* is the viscous length scale) when accurately determined measurements reaching y+=5 and 10, respectively, are available. In the absence of data below the above given limits, commonly employed analytical functions and their log law constants, have been found to affect the the determination of wall position to a high degree. It has been shown, that near-wall measurements below y+=10 or preferable 5 are essential in order to ensure a correctly measured or deduced absolute wall position. A number of peculiarities in concurrent wall-bounded turbulent flow studies, was found to be associated with a erroneously deduced wall position. The effect of poor spatial resolution using hot-wire anemometry on the measurements of the streamwise velocity is dealt with in the last part. The viscous scaled hot-wire length, L+, has been found to exert a strong impact on the probability density distribution (pdf) of the streamwise velocity, and hence its higher order moments, over the entire buffer region and also the lower region of the log region. For varying Reynolds numbers spatial resolution effects act against the trend imposed by the Reynolds number. A systematic reduction of the mean velocity with increasing L+ over the entire classical buffer region and beyond has been found. A reduction of around 0.3 uƬ, where uƬ is the friction velocity, has been deduced for L+=60 compared to L+=15. Neglecting this effect can lead to a seemingly Reynolds number dependent buffer or log region. This should be taken into consideration, for instance, in the debate, regarding the prevailing influence of viscosity above the buffer region at high Reynolds numbers. We also conclude that the debate concerning the universality of the pdf within the overlap region has been artificially complicated due to the ignorance of spatial resolution effects beyond the classical buffer region on the velocity fluctuations.<br>QC 20100820
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Li, Qiang. "Direct and Large-Eddy Simulations of Turbulent Boundary Layers with Heat Transfer." Doctoral thesis, KTH, Mekanik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-41156.
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Yang, Qin. "Computational study of sound generation by surface roughness in turbulent boundary layers." Thesis, University of Notre Dame, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3578996.
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<p> Noise generated by flow over rough surfaces is an important issue in naval applications and in aeronautical engineering. This work numerically investigates roughness-induced noise from low-Mach-number turbulent boundary layers. The computational approach is based on Lighthill's acoustic analogy with acoustic sources obtained from large-eddy simulation. An acoustic formulation is derived, which shows that each roughness element acts as an individual in-plane dipole source strengthened by its image in the wall. Flow configurations investigated include boundary-layer flows over a single hemispherical roughness element, a pair of streamwisely aligned hemispherical elements and three roughness fetches consisting of 10 × 4 hemispherical, cuboidal and cylindrical roughness elements, respectively.</p><p> Results for a single hemispherical roughness element and a pair of hemispherical elements show that the spanwise dipole, which has been overlooked before, is of larger or similar strength compared to the streamwise dipole. The viscous contribution to the dipoles is negligible compared to the pressure contribution. The main sound sources arise from the impingement of incoming turbulence and the unsteady horse-shoe vortices generated around the element. The roughness-induced unsteady wake motions are unimportant as a source of self noise. However, they significantly enhance sound radiation from a downstream hemisphere.</p><p> The effects of multi-element interactions and the roughness shape are investigated with arrays of 10 × 4 sparsely distributed hemispheres, cuboids and short cylinders. The dipole strength, orientation and spatial distribution show strong dependence on the roughness shape. Correlations between dipole sources associated with neighboring elements are found to be small for these sparsely distributed roughness arrays. Correlations and coherence between roughness dipoles and surface pressure fluctuations are analyzed, which reveals the importance of the impingement of upstream turbulence and surrounding vortical structures to dipole sound radiation, especially in the streamwise direction. For roughness shapes with sharp frontal edges, the edge-induced unsteady separation and reattachment also play important roles in sound generation. Large-scale turbulent structures in the boundary layer have a relatively low influence on roughness dipoles, except for the first row of elements.</p>
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Zhang, Yufang. "Coupled convective heat transfer and radiative energy transfer in turbulent boundary layers." Phd thesis, Ecole Centrale Paris, 2013. http://tel.archives-ouvertes.fr/tel-00969159.
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If radiation plays an important role in many engineering applications, especially in those including combustion systems, influence of radiation on turbulent flows, particularly on the turbulent boundary layers, is still not well known. The objective is here to perform a detailed study of radiation effect on turbulent flows. An optimized emission-based reciprocal (OERM) approach of the Monte-Carlo method is proposed for radiation simulation using the CK model for radiative gas properties. OERM allows the uncertainty of results to be locally controlled while it overcomes the drawback of the original emission-based reciprocity approach by introducing a new frequency distribution function that is based on the maximum temperature of the domain. Direct Numerical Simulation (DNS) has been performed for turbulent channel flows under different pressure, wall temperatures and wall emissivity conditions. Flow field DNS simulations are fully coupled with radiation simulation using the OERM approach. The role of radiation on the mean temperature field and fluctuation field are analyzed in details. Modification of the mean temperature profile leads to changes in wall conductive heat fluxes and new wall laws for temperature when radiation is accounted for. The influence on temperature fluctuations and the turbulent heat flux is investigated through their respective transport equations whose balance is modified by radiation. A new wall-scaling based on the energy balance is proposed to improve collapsing of wall-normal turbulent flux profiles among different channel flows with/without considering radiation transfer. This scaling enables a new turbulent Prandtl number model to be introduced to take into account the effects of radiation. In order to consider the influence of radiation in the near-wall region and predict the modified wall law, a one-dimensional wall model for Large Eddy Simulation (LES) is proposed. The 1D turbulent equilibrium boundary layer equations are solved on an embedded grid in the inner layer. The obtained wall friction stress and wall conductive flux are then fed back to the LES solver. The radiative power term in the energy equation of the 1D wall model is computed from an analytical model. The proposed wall model is validated by a comparison with the former DNS/Monte-Carlo results. Finally, two criteria are proposed and validated. The first one is aimed to predict the importance of wall radiative heat flux while the other one predicts whether a wall model accounting for radiation in the near wall region is necessary. A parametric study is then performed where a k-ǫ model and a turbulent Prandtl number model are applied to simulate the velocity and temperature field of different channel flows under various flow conditions. The obtained criteria values are analyzed and compared.
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Kerevanian, G. K. "Experimental investigation of turbulent boundary layers on uniform, well-defined rough walls." Thesis, Queen's University Belfast, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269051.
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Khatir, Zinedine. "Discrete vortex modelling of near-wall flow structures in turbulent boundary layers." Thesis, University of Warwick, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364578.
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Pearce, Nicholas F. "An investigation of turbulent boundary layers with streamwise and spanwise pressure gradients." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/57513/.
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An experimental comparison is made between two turbulent boundary layers produced in a low-speed water channel subjected to different pressure gradient distributions. Both flows involve identical favourable streamwise components, generated via a lateral contraction of the flow area; and in the second case, an additional spanwise gradient is imposed by curving the walls. The measurement system and methods are developed in full, with rigorous testing and validation allowing the uncertainty and accuracy of the results to be estimated. Hot-wire anemometry is employed to take measurements of velocity using miniature single-film probes. A Hydrogen bubble visualisation system enables an inspection of the coherent turbulent structures in the boundary layer near the wall. The mean-velocity measurements show a continued rise in the Reynolds number downstream accompanied by a fall in the coefficient of friction, in spite of a relatively high streamwise acceleration. This unorthodox behaviour was found to occur for both flows. In response to the acceleration, changes in the statistical moments of streamwise velocity show an increased dominance of high velocity fluctuations near the wall. This corresponds with the results of the structure visualisations which reveal a rise in the mean spanwise spacing of the low-speed fluid elements. The pressure gradients of the two cases are generated using a novel approach which aims to make the effects from each strain easier to evaluate. The additional spanwise component in the second case induced a cross ow in the boundary layer which reached 11% that of the local external velocity. Despite this, the measurements and low-speed streaks show the turbulence to be relatively insensitive to this level of three-dimensionality. A simple numerical method is presented to model the development of the low-speed fluid streaks in different mean-velocity distributions. Using this model, greater cross flow magnitudes in the boundary layer are tested for which a positive streak dependence is found.
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Goody, Michael. "An Experimental Investigation of Pressure Fluctuations in Three-Dimensional Turbulent Boundary Layers." Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/29908.
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This dissertation presents experimental measurements and analysis of the surface pressure fluctuations beneath several turbulent boundary layers of practical interest. Pressure fluctuations in turbulent boundary layers are a source of noise and vibration that can accelerate structural fatigue. Pressure fluctuations and their correlation with velocity fluctuations is an important diffusive mechanism of turbulence transport. The approach was to study the statistics of both the surface pressure and the velocity field through new measurements of the fluctuating surface pressure and existing measurements of the velocity field and the covariance of the surface pressure and fluctuating velocity components.
Measurements were made in three types of flows. The first type of flow was a zero pressure gradient, two-dimensional, turbulent boundary layer (Re(theta) = 7300 and Re(theta) = 23400). The two-dimensional flows serve as a baseline for comparison to the other three-dimensional flows and validate the experimental techniques used in the present study through comparison with existing measurements. The second type of flow was a three-dimensional, pressure-driven, turbulent boundary layer that forms away from a wing-body junction. Two of this type of boundary layer were studied - Re(theta) = 5940 and Re(theta) = 23200. The third type of flow was the separating flow about the leeside of a 6:1 prolate spheroid at angle of attack. Measurements were made at two angles of attack, 10° and 20°, and two axial locations, x/L = 0.600 and x/L = 0.772, in this type of flow.
Spectral scaling is discussed and various scaling combinations of the spectral power density of surface pressure fluctuations beneath two-dimensional boundary layers that cover a wide range of Reynolds number (1400 < Re(theta) < 23400) are presented. The spectral power density of surface pressure fluctuations beneath the separating flow on the leeside of a 6:1 prolate spheroid at 10° angle of attack collapse when normalized using viscous scales. However, the spectral power density of surface pressure fluctuations beneath highly three-dimensional flow contain nearly constant spectral levels within a middle to high frequency range. The nearly constant spectral levels are due to a lack of overlapping frequency structure between the large-scale motions and the viscous-dominated motions since each of these types of motion may have different flow histories due to the three-dimensional flow structure. This effect amplifies the importance of the middle frequency range to p' as compared to two-dimensional flows. In terms of instrumentation, accurate p' measurements in a three-dimensional flow require accurate high frequency (f > 20 kHz) p measurements.
The lack of similarity in the shape of the spectral power density preclude a direct extension of "universal" generalizations that are true for surface pressure fluctuations beneath two-dimensional boundary layers. The resulting RMS surface pressure fluctuation distributions reflect the importance of the high frequency wall region contributions. Scaling parameters for the p spectra beneath three-dimensional flows must incorporate local flow structure in order to be successful. Analysis based on the Poisson equation shows that variation of the high frequency spectral levels are related to the variation in near-wall mean velocity gradients and v² structure. In the 6:1 prolate spheroid flow, near regions of crossflow separation there is a local minimum in RMS surface pressure fluctuations, whereas around reattachments and under the large shed vortices there is a local maximum in RMS surface pressure fluctuations.
Measurements of the correlation coefficient between surface pressure and velocity fluctuations show that there can be sources of p away from the wall in three-dimensional flows. Sources of p away from the wall are significant in terms of fluid-structure interaction since they contribute low frequency fluctuations. Structures typically have low resonant frequencies. Sources of p away from the wall are also significant in terms of radiated sound since they are likely to interact with the free-stream and be radiated away as sound.<br>Ph. D.
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Örlü, Ramis. "Experimental studies in jet flows and zero pressure-gradient turbulent boundary layers /." Stockholm : Skolan för teknikvetenskap, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10448.
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Alonso, pinar Alberto. "Aero and vibroacoustical prediction of the noise generated by turbulent boundary layers." Thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-261180.
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Flow noise is a major noise source in the transportation industry from the automotive up to the aircraft industry. The characterization of the aerodynamic excitations and of the structure transmission is of primary interest in order to improve the passenger and crew comfort. One important component of the flow noise excitation comes from the wall pressure fluctuations induced by the development of turbulent boundary layers around the vehicle. This master thesis is focused on the validation of a method to calculate structural vibrations based on aerodynamic data by the comparison with experimental data. The analysis will be done with a flat plate configuration in a wind tunnel. The strategy yields good results and it has been validated: it could be used for more complex problems.
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Hytopoulos, Evangelos. "A turbulence model for steady and unsteady boundary layers in strong pressure gradients." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/40119.
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A new turbulence model designed for two-dimensional, steady and unsteady boundary layers in strong adverse pressure gradients is described. The model is developed in a rational way based on an understanding of the flow physics obtained from recent experimental observations. The turbulent shear stress is given by a mixing length model, but the variation of the mixing length in the outer region is not constant; it varies according to an integral form of the turbulence kinetic-energy equation. This approach allows for the history effects of the turbulence to be taken into account in an approximate but rational way. The form of the near-wall mixing length model is derived based on the rigorous distribution of the shear stress near the wall, and it takes into account the pressure and convection terms which become important in strong adverse pressure gradients. Since the significance of the normal stresses in turbulent kinetic-energy production is increasing as separation is approached, a model accounting for this contribution is incorporated. The model is calibrated using available experimental data. These data also indicate a change in turbulence structure near and through separation. Such a change can be significant and is accounted for here using an empirical function. The complete model was tested against steady and unsteady, two-dimensional experimental cases with adverse pressure gradient up to separation. Improved predictions compared to those obtained with other turbulence models were demonstrated. The general and rational approach that led to the derivation of the model allows the straightforward extension of the model in the region of separation. The further extension to steady and unsteady, three-dimensional cases is indicated.<br>Ph. D.
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Zhong, Shan. "An interferometric study of organized structures in compressible turbulent flows." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319551.
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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.<br>Ph. D.
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Arasanipalai, Sriram Sharan. "Two-equation model computations of high-speed (ma=2.25, 7.2), turbulent boundary layers." Thesis, [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3186.
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Mare, Chris. "Effects of stratification on flow and dispersion around obstacles in turbulent boundary layers." Thesis, University of Surrey, 2003. http://epubs.surrey.ac.uk/844132/.
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The effects of stability on the flow and dispersion downstream of a simple obstacle were studied experimentally. Experiments were conducted in the EnFlo atmospheric wind tunnel, where a stably stratified boundary layer is set up by heating the inlet air and cooling the floor of the wind tunnel. Neutral and stable boundary layers with different measures of stability have been successfully modelled and their measured characteristics are reported. The majority of the experiments were then conducted with a neutral boundary layer with a nominal freestream velocity of 2.5 m/s, and two stable boundary layers with nominal freestream velocities of 1.3 m/s and 1.1 m/s. The obstacle used throughout was a 100 mm cube, placed normal to the flow direction and at 45° to the flow direction. A pressure tapped version of the cube was placed in the neutral and stably stratified boundary layers and the pressure distribution was measured on the surface of the cube for each case. Flow measurements were also made in the wake of the cube for the neutral and two stable boundary layers. Concentration measurements were made for different release locations and the flow configurations described above. The source was placed at the leading edge, and source heights at ground level, equal to the obstacle height, and 50% higher than the obstacle height were used. The results and statistics reported here are vertical profiles of concentration, concentration fluctuations and concentration flux, vertical and horizontal plume spread, centreline ground level concentrations and probability distributions. A simple three dimensional wake theory typically used in dispersion modelling was evaluated and the assumptions associated with it reviewed. A Gaussian dispersion model incorporating a building effects model based on the wake theory was then implemented in a computer program. Comparisons were made between the measured and the modelled ground level concentrations. The building effects modelling was then isolated by using the experimental undisturbed plume spread results in the model.
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Lanspeary, Peter V. "Establishing very low speed, disturbance-free flow for anemometry in turbulent boundary layers." Title page, contents and summary only, 1997. http://web4.library.adelaide.edu.au/theses/09PH/09phl295.pdf.
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Thesis (Ph. D.)--University of Adelaide, Dept. of Mechanical Engineering, 1998?<br>System requirements for accompanying computer disks: IBM-compatible computer. Other requirements: Fortran and/or C Compiler. Includes bibliographical references (p. 315-330).
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Hutchins, Nick. "An investigation of larger scale coherent structures in fully developed turbulent boundary layers." Thesis, University of Nottingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289311.
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