The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
John K. Eaton - One of the best experts on this subject based on the ideXlab platform.
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Reynolds Number scaling of the flat plate turbulent boundary layer
Journal of Fluid Mechanics, 2000Co-Authors: David B De Graaff, John K. EatonAbstract:Despite extensive study, there remain significant questions about the Reynolds-Number scaling of the zero-pressure-gradient flat-plate turbulent boundary layer. While the mean flow is generally accepted to follow the law of the wall, there is little consensus about the scaling of the Reynolds normal stresses, except that there are Reynolds-Number effects even very close to the wall. Using a low-speed, high-Reynolds-Number facility and a high-resolution laser-Doppler anemometer, we have measured Reynolds stresses for a flat-plate turbulent boundary layer from Re θ = 1430 to 31 000. Profiles of u ′ 2 , v ′ 2 , and u ′ v ′ show reasonably good collapse with Reynolds Number: u ′ 2 in a new scaling, and v ′ 2 and u ′ v ′ in classic inner scaling. The log law provides a reasonably accurate universal profile for the mean velocity in the inner region.
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The effect of Reynolds Number on boundary layer turbulence
Experimental Thermal and Fluid Science, 1998Co-Authors: D. B. Degraaff, Donald R. Webster, John K. EatonAbstract:Abstract A new facility for studying high Reynolds Number incompressible turbulent boundary layer flows has been constructed. It consists of a moderately sized wind tunnel, completely enclosed by a pressure vessel, which can raise the ambient air pressure in and around the wind tunnel to 8 atmospheres. This results in a Reynolds Number range of about 20:1, while maintaining incompressible flow. Results are presented for the zero pressure gradient flat plate boundary layer over a momentum thickness Reynolds Number range 1500–15 000. Scaling issues for high Reynolds Number non-equilibrium boundary layers are discussed, with data comparing the three-dimensional turbulent boundary layer flow over a swept bump at Reynolds Numbers of 3800 and 8600. It is found that successful prediction of these types of flows must include length scales which do not scale on Reynolds Number, but are inherent to the geometry of the flow.
Ivan Marusic - One of the best experts on this subject based on the ideXlab platform.
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high Reynolds Number wall turbulence
Annual Review of Fluid Mechanics, 2011Co-Authors: Alexander Smits, B. J. Mckeon, Ivan MarusicAbstract:We review wall-bounded turbulent flows, particularly high–Reynolds Number, zero–pressure gradient boundary layers, and fully developed pipe and channel flows. It is apparent that the approach to an asymptotically high–Reynolds Number state is slow, but at a sufficiently high Reynolds Number the log law remains a fundamental part of the mean flow description. With regard to the coherent motions, very-large-scale motions or superstructures exist at all Reynolds Numbers, but they become increasingly important with Reynolds Number in terms of their energy content and their interaction with the smaller scales near the wall. There is accumulating evidence that certain features are flow specific, such as the constants in the log law and the behavior of the very large scales and their interaction with the large scales (consisting of vortex packets). Moreover, the refined attached-eddy hypothesis continues to provide an important theoretical framework for the structure of wall-bounded turbulent flows.
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High–Reynolds Number Wall Turbulence
Annual Review of Fluid Mechanics, 2011Co-Authors: Alexander J. Smits, B. J. Mckeon, Ivan MarusicAbstract:We review wall-bounded turbulent flows, particularly high?Reynolds Number, zero?pressure gradient boundary layers, and fully developed pipe and channel flows. It is apparent that the approach to an asymptotically high?Reynolds Number state is slow, but at a sufficiently high Reynolds Number the log law remains a fundamental part of the mean flow description. With regard to the coherent motions, very-large-scale motions or superstructures exist at all Reynolds Numbers, but they become increasingly important with Reynolds Number in terms of their energy content and their interaction with the smaller scales near the wall. There is accumulating evidence that certain features are flow specific, such as the constants in the log law and the behavior of the very large scales and their interaction with the large scales (consisting of vortex packets). Moreover, the refined attached-eddy hypothesis continues to provide an important theoretical framework for the structure of wall-bounded turbulent flows.
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High Reynolds Number effects in wall turbulence
International Journal of Heat and Fluid Flow, 2010Co-Authors: Ivan Marusic, Romain Mathis, Nicholas HutchinsAbstract:A review of recent advances in the study of high Reynolds Number turbulent boundary layers is given. The emergent regime of very large-scale structures in the logarithmic region and their subsequent influence on the near-wall cycle challenges many of the previously held assumptions regarding scaling of turbulent boundary layers at high Reynolds Numbers. Experimental results are presented to illustrate the superimposition of large-scale energy onto the near-wall cycle, together with an interaction well described by an amplitude modulation effect. Both phenomena are shown to increase in magnitude (as compared to viscous-scaled events) as Reynolds Number increases. These observations lead to a possible model for a statistically representative near-wall velocity signal (giving accurate energy spectra) based on a given filtered velocity signal from the log region of a high Reynolds Number turbulent flow.
David B De Graaff - One of the best experts on this subject based on the ideXlab platform.
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Reynolds Number scaling of the flat plate turbulent boundary layer
Journal of Fluid Mechanics, 2000Co-Authors: David B De Graaff, John K. EatonAbstract:Despite extensive study, there remain significant questions about the Reynolds-Number scaling of the zero-pressure-gradient flat-plate turbulent boundary layer. While the mean flow is generally accepted to follow the law of the wall, there is little consensus about the scaling of the Reynolds normal stresses, except that there are Reynolds-Number effects even very close to the wall. Using a low-speed, high-Reynolds-Number facility and a high-resolution laser-Doppler anemometer, we have measured Reynolds stresses for a flat-plate turbulent boundary layer from Re θ = 1430 to 31 000. Profiles of u ′ 2 , v ′ 2 , and u ′ v ′ show reasonably good collapse with Reynolds Number: u ′ 2 in a new scaling, and v ′ 2 and u ′ v ′ in classic inner scaling. The log law provides a reasonably accurate universal profile for the mean velocity in the inner region.
S. M. B. Rivers - One of the best experts on this subject based on the ideXlab platform.
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Off-Design Reynolds Number Effects for a Supersonic Transport
2013Co-Authors: L. R. Owens, R. A. Wahls, S. M. B. RiversAbstract:A high-Reynolds-Number wind-tunnel investigation was conducted to assess Reynolds-Number effects on the aerodynamic performance characteristics of a realistic, second-generation, supersonic transport concept. The tests included longitudinal studies at transonic and low-speed, high-lift conditions across a range of chord Reynolds Numbers (8 x 10 6 to 120 x 10 6 ). Results presented focus on Reynolds-Number and static aeroelastic sensitivities at Mach 0.30 and 0.90 for a configuration without a tail. Static aeroelastic effects, which mask Reynolds-Number effects, were observed. Reynolds-Number effects were generally small, and the drag data followed established trends of skin friction as a function of Reynolds Number. Wing boundary layers thinned as Reynolds Number increased producing a more nose-down pitching moment because of the increased effective wing camber. This study extends the existing Reynolds-Number database for supersonic transports operating at off-design conditions.
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Reynolds Number Effects on a Supersonic Transport at Transonic Conditions
39th Aerospace Sciences Meeting and Exhibit, 2001Co-Authors: R. A. Wahls, L. R. Owens, S. M. B. RiversAbstract:A High Speed Civil Transport configuration was tested in the National Transonic Facility at the High Speed Research Program. The primary purposes of the tests were to assess Reynolds Number scale effects and the high Reynolds Number aerodynamic characteristics of a realistic, second generation supersonic transport while providing data for the assessment of computational methods. The tests included longitudinal and lateral/directional studies at low-speed high-lift and transonic conditions across a range of Reynolds Numbers from that available in conventional wind tunnels to near flight conditions. Results are presented which focus on both the Reynolds Number and static aeroelastic sensitivities of longitudinal characteristics at Mach 0.90 for a configuration without an empennage.
Promode R. Bandyopadhyay - One of the best experts on this subject based on the ideXlab platform.
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Vortex Reynolds Number in turbulent boundary layers
Theoretical and Computational Fluid Dynamics, 1995Co-Authors: Promode R. Bandyopadhyay, R. BalasubramanianAbstract:The effects of vortex Reynolds Number on the statistics of turbulence in a turbulent boundary layer have been investigated. Vortex Reynolds Number is defined as the ratio of circulation around the vortex structure to the fluid viscosity. The vortex structure of the outer region was modeled and a full numerical simulation was then conducted using a high-order spectral method. A unit domain of the outer region of a turbulent boundary layer was assumed to be composed of essentially three elements: a wall, a Blasius mean shear, and an elliptic vortex inclined at 45° to the flow direction. The laminar base-flow Reynolds Number is roughly in the same range as that of a turbulent boundary layer based on eddy viscosity, and the vortex-core diameter based on the boundary-layer thickness is nearly the same as the maximum mixing length in a turbulent boundary layer. The computational box size, namely, 500, 150, and 250 wall units in the streamwise, surface-normal, and spanwise directions, respectively, is approximately the same as the measured quasi-periodic spacings of the near-wall turbulence-producing events in a turbulent boundary layer. The effects of vortex Reynolds Number and the signs of the circulation on the moments of turbulence were examined. The signs mimic the ejection and sweep types of organized motions of a turbulent boundary layer. A vortex Reynolds Number of 200 describes the turbulence moments in the outer layer reasonably well.
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Reynolds Number Effects in Wall-Bounded Turbulent Flows
Applied Mechanics Reviews, 1994Co-Authors: Promode R. BandyopadhyayAbstract:This paper reviews the state of the art of Reynolds Number effects in wall-bounded shear-flow turbulence, with particular emphasis on the canonical zero-pressure-gradient boundary layer and two-dimensional channel flow problems. The Reynolds Numbers encountered in many practical situations are typically orders of magnitude higher than those studied computationally or even experimentally. High-Reynolds Number research facilities are expensive to build and operate and the few existing are heavily scheduled with mostly developmental work. For wind tunnels, additional complications due to compressibility effects are introduced at high speeds. Full computational simulation of high-Reynolds Number flows is beyond the reach of current capabilities. Understanding of turbulence and modeling will continue to play vital roles in the computation of high-Reynolds Number practical flows using the Reynolds-averaged Navier-Stokes equations. Since the existing knowledge base, accumulated mostly through physical as well as numerical experiments, is skewed towards the low Reynolds Numbers, the key question in such high-Reynolds Number modeling as well as in devising novel flow control strategies is: what are the Reynolds Number effects on the mean and statistical turbulence quantities and on the organized motions? Since the mean flow review of Coles (1962), the coherent structures, in low-Reynolds Number wall-bounded flows, have been reviewed several times. However, the Reynolds Number effects on the higher-order statistical turbulence quantities and on the coherent structures have not been reviewed thus far, and there are some unresolved aspects of the effects on even the mean flow at very high Reynolds Numbers. Furthermore, a considerable volume of experimental and full-simulation data have been accumulated since 1962. The present article aims at further assimilation of those data, pointing to obvious gaps in the present state of knowledge and highlighting the misunderstood as well as the ill-understood aspects of Reynolds Number effects.
