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Jeanphilippe Laval - One of the best experts on this subject based on the ideXlab platform.
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experimental measurements of a high reynolds number Adverse Pressure Gradient turbulent boundary layer
Bulletin of the American Physical Society, 2016Co-Authors: C Aktinson, Michel Stanislas, Jeanphilippe Laval, Rainer Hain, Christophe Cuvier, Jeanmarc Foucaut, Omid Amili, S Srinath, Christian Kaehler, Sven ScharnovskiAbstract:The study of Adverse Pressure Gradient turbulent boundary layers is complicated by the need to characterise both the local Pressure Gradient and it’s upstream flow history. It is therefore necessary to measure a significant streamwise domain at a resolution sufficient to resolve the small scales features. To achieve this collaborative particle image velocimetry (PIV) measurements were performed in the large boundary layer wind-tunnel at the Laboratoire de Mecanique de Lille, including: planar measurements spanning a streamwise domain of 3.5m using 16 cameras covering 15δ; spanwise wall-normal stereo-PIV measurements, high-speed micro-PIV of the near wall region and wall shear stress; and streamwise wall-normal PIV in the viscous sub layer. Details of the measurements and preliminary results will be presented.
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an assessment of attached and mildly separated flows in Adverse Pressure Gradient regions
52nd Aerospace Sciences Meeting, 2014Co-Authors: Antonio B Jesus, Joao Luiz F Azevedo, Luiz Augusto C Schiavo, Jeanphilippe LavalAbstract:The work presents comparative results between wall friction and Pressure coefficient predictions from Large Eddy Simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) computations in channel flows with an Adverse Pressure Gradient created by a 2-D bump. LES results are obtained using the semi-spectral code, MFLOPS3D, developed at Laboratoire de Mecanique de Lille, while RANS solutions are computed using a commercial code based on 2nd-order finite volume discretization with typical two-equation turbulence models and one seven-equation Reynolds stress transport model. Reynolds numbers range from Reτ = 617 to 2000, based on the friction velocity at the channel inlet. It is found that LES produces very consistent results when compared to DNS or other highly resolved LES. Two-equation and seven-equation RANS models are found to correctly predict friction coefficients in zero and favorable Pressure Gradient regions, but they fail in regions of Adverse Pressure Gradients. The Reynolds stress transport model shows a better performance when compared to two-equation eddy-viscosity models, particularly in the higher Reynolds number cases. However, none of the RANS models is able to capture the full physics of turbulence related with Adverse Pressure Gradients. The limitations of RANS models are observed both in separated and attached flow conditions at the rear portion of the bump. Such limitations seem to be related to the fact that these models do not correctly describe the evolution of the turbulent kinetic energy close to the walls in Adverse Pressure Gradient regions.
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large eddy simulations and rans computations of Adverse Pressure Gradient flows
51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2013Co-Authors: Antonio B Jesus, Joao Luiz F Azevedo, Jeanphilippe LavalAbstract:The work presents comparative results between wall friction coe cient predictions from Large Eddy Simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) computations in channel ows with an Adverse Pressure Gradient created by a two-dimensional bump. LES results are obtained using the semi-spectral code, MFLOPS3D, developed at Laboratoire de M ecanique de Lille (LML), while RANS solutions are computed using a commercial code based on 2nd-order nite volume discretization with typical two-equation turbulence models and one seven-equation Reynolds stresses transport model. Computations are performed in two bump pro les installed in a channel. Reynolds numbers range from Re = 617 to 950 based on the friction velocity at the channel inlet. It is found that LES produces very consistent results when compared to DNS or other highly resolved LES. On the other hand, RANS models are found to predict an incorrect evolution of the friction coe cient in regions of Adverse Pressure Gradient, even if separation or re-attachment locations are correctly predicted. This limitation of RANS models is observed both in separated and attached ow situations and it seems to be related to the fact that these models do not correctly describe the evolution of the turbulent kinetic energy close to the walls in Adverse Pressure Gradient regions.
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new insights into Adverse Pressure Gradient boundary layers
Bulletin of the American Physical Society, 2012Co-Authors: William K George, Michel Stanislas, Jeanphilippe LavalAbstract:We hypothesize that far enough downstream the mean velocity profile in any non − separating Adverse Pressure Gradient turbulent bounday layer will become inflectional. While this evolution is underway a universal scaling for the outer flow is impossible. Once the profile is fully-developed, however, there is significant support for the Castillo/George [2, 4] theory.
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a specific behaviour of Adverse Pressure Gradient near wall flows
2011Co-Authors: Syedimran Shah, Jeanphilippe Laval, Michel StanislasAbstract:Adverse Pressure Gradient turbulent flows are of prime importance for aeronautics as they are characteristic of the suction side flow along an airfoil at any positive angle of attack. These flows have been known for a long time to pose modelling problems. The turbulence behaviour departs significantly from the standard near wall turbulence (as observed in flat plate boundary layers and channels). In diffusers, as well as in boundary layers, the flow separates from the wall as soon as the Adverse Pressure Gradient is strong enough. In the present contribution, a few selected data from the literature are reviewed and compared together and with a recent DNS of converging–diverging channel flow performed in the frame of the WALLTURB project. This simulation provides data on APG near wall flow, both with and without curvature. The analysis of these data indicates that an instability is developing inside the turbulent near wall flow in both cases. The comparison of turbulent statistics with the data from the literature indicates that this phenomenon is fairly general in APG near wall flows.
Michel Stanislas - One of the best experts on this subject based on the ideXlab platform.
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experimental measurements of a high reynolds number Adverse Pressure Gradient turbulent boundary layer
Bulletin of the American Physical Society, 2016Co-Authors: C Aktinson, Michel Stanislas, Jeanphilippe Laval, Rainer Hain, Christophe Cuvier, Jeanmarc Foucaut, Omid Amili, S Srinath, Christian Kaehler, Sven ScharnovskiAbstract:The study of Adverse Pressure Gradient turbulent boundary layers is complicated by the need to characterise both the local Pressure Gradient and it’s upstream flow history. It is therefore necessary to measure a significant streamwise domain at a resolution sufficient to resolve the small scales features. To achieve this collaborative particle image velocimetry (PIV) measurements were performed in the large boundary layer wind-tunnel at the Laboratoire de Mecanique de Lille, including: planar measurements spanning a streamwise domain of 3.5m using 16 cameras covering 15δ; spanwise wall-normal stereo-PIV measurements, high-speed micro-PIV of the near wall region and wall shear stress; and streamwise wall-normal PIV in the viscous sub layer. Details of the measurements and preliminary results will be presented.
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new insights into Adverse Pressure Gradient boundary layers
Bulletin of the American Physical Society, 2012Co-Authors: William K George, Michel Stanislas, Jeanphilippe LavalAbstract:We hypothesize that far enough downstream the mean velocity profile in any non − separating Adverse Pressure Gradient turbulent bounday layer will become inflectional. While this evolution is underway a universal scaling for the outer flow is impossible. Once the profile is fully-developed, however, there is significant support for the Castillo/George [2, 4] theory.
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a specific behaviour of Adverse Pressure Gradient near wall flows
2011Co-Authors: Syedimran Shah, Jeanphilippe Laval, Michel StanislasAbstract:Adverse Pressure Gradient turbulent flows are of prime importance for aeronautics as they are characteristic of the suction side flow along an airfoil at any positive angle of attack. These flows have been known for a long time to pose modelling problems. The turbulence behaviour departs significantly from the standard near wall turbulence (as observed in flat plate boundary layers and channels). In diffusers, as well as in boundary layers, the flow separates from the wall as soon as the Adverse Pressure Gradient is strong enough. In the present contribution, a few selected data from the literature are reviewed and compared together and with a recent DNS of converging–diverging channel flow performed in the frame of the WALLTURB project. This simulation provides data on APG near wall flow, both with and without curvature. The analysis of these data indicates that an instability is developing inside the turbulent near wall flow in both cases. The comparison of turbulent statistics with the data from the literature indicates that this phenomenon is fairly general in APG near wall flows.
R. A. W. M. Henkes - One of the best experts on this subject based on the ideXlab platform.
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computations of a turbulent wake in a strong Adverse Pressure Gradient
International Journal of Heat and Fluid Flow, 2007Co-Authors: M J Tummers, D. M. Passchier, K Hanjalic, R. A. W. M. HenkesAbstract:Abstract Numerical solutions of the Reynolds-averaged Navier–Stokes equations are presented for the near wake of a flat plate with and without the effects of an Adverse Pressure Gradient. The comparison with experiments indicates that both the standard k – ϵ model and a Reynolds-stress transport model accurately reproduce the centreline velocity and the turbulent kinetic energy in the zero-Pressure-Gradient near wake. In the Adverse-Pressure-Gradient wake, however, none of the turbulence models tested was able to predict the measured mean-flow reversal near the centreline, and the large rise in turbulence kinetic energy in the wake. Examination of the measured and computed kinetic energy budgets in the wake indicated that this discrepancy is due to an incorrect response of the dissipation equation to a spectral imbalance noticed in the experiments.
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linear and nonlinear development of localized disturbances in zero and Adverse Pressure Gradient boundary layers
Physics of Fluids, 1998Co-Authors: Knut H Bech, Dan S Henningson, R. A. W. M. HenkesAbstract:Localized disturbances in laminar boundary-layers at Reynolds number Reδ*=950 were studied using direct numerical simulation. Instability mechanisms in both an Adverse and zero Pressure Gradient were investigated by introducing three different three-dimensional disturbances. The first disturbance was centered around a pair of oblique waves in Fourier space, the second around a plane wave, while the third was axisymmetric. For small amplitudes, the first disturbance developed into a wave-packet of oblique waves in Adverse Pressure Gradient and into a streaky structure with a trailing wave-packet in a zero Pressure Gradient. The second disturbance developed into a wave-packet centered around plane waves in both Pressure Gradients. The third disturbance developed into a wave-packet of plane waves in Adverse Pressure Gradient and, due to the transient growth mechanism, into a streaky structure in a zero Pressure Gradient. For finite-amplitude plane wave-packets in a zero Pressure Gradient, a subharmonic secon...
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Natural Transition in an Adverse Pressure Gradient Boundary Layer
Advances in Turbulence VI, 1996Co-Authors: B. F. A. Van Hest, D. M. Passchier, R. A. W. M. HenkesAbstract:The paper is devoted to an experimental study of the natural transition process in boundary layers subjected to an Adverse Pressure Gradient and low free stream turbulence intensity. The study was performed to obtain several goals. The first was to extend the available data-set of transitional boundary layers under Adverse Pressure Gradient with detailed measurements of the streamwise and wall-normal velocity components (mean values and Reynolds stresses), velocity spectra, and measurements of the intermittency across the boundary layer and in the streamwise direction. The velocity spectra were used to verify the applicability of linear stability theory, (especially with respect to the parallel-flow assumption with fast boundary layer growth) and the possible effects of nonlinear interaction (because of the large amplification rates) on transition prediction. The measurements of the intermittency were used to verify available empirical relations, like Klebanoff’s (1956) and Narasimha’s (1957) intermittency distributions, which are often used in models for the flow in the transition region.
Flint O Thomas - One of the best experts on this subject based on the ideXlab platform.
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an experimental investigation of an unsteady Adverse Pressure Gradient turbulent boundary layer embedded shear layer scaling
Journal of Fluid Mechanics, 2017Co-Authors: D M Schatzman, Flint O ThomasAbstract:An experimental investigation of an unsteady Adverse Pressure Gradient turbulent boundary layer is described. It is demonstrated that the local flow physics is largely dominated by an inflectional instability which gives rise to an embedded shear layer contained within the boundary layer. Experimental measurements are presented which are fully consistent with the presence of clockwise spanwise-oriented coherent vorticity within the embedded shear layer. Using embedded shear layer scaling parameters in the form of the shear layer vorticity thickness and the velocity defect at the upper inflection point, both the mean and the phase-averaged boundary layer velocity profiles exhibit similarity in both space and time over a large wall-normal extent. In a similar manner, the profiles of the streamwise-component turbulence intensity and Reynolds stress also exhibit similarity when scaled with the embedded shear layer parameters. The embedded shear layer scaling of previously published Adverse Pressure Gradient turbulent boundary layer measurements confirms its generic applicability in a wide range of flow-field geometries and extending to high Reynolds numbers.
Alexander Smits - One of the best experts on this subject based on the ideXlab platform.
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a supersonic turbulent boundary layer in an Adverse Pressure Gradient
Journal of Fluid Mechanics, 1990Co-Authors: Emerick M Fernando, Alexander SmitsAbstract:This investigation describes the effects of an Adverse Pressure Gradient on a flat plate supersonic turbulent boundary layer ( M f ≈ 2.9, β x ≈ 5.8, Re θ, ref ≈ 75600). Single normal hot wires and crossed wires were used to study the Reynolds stress behaviour, and the features of the large-scale structures in the boundary layer were investigated by measuring space–time correlations in the normal and spanwise directions. Both the mean flow and the turbulence were strongly affected by the Pressure Gradient. However, the turbulent stress ratios showed much less variation than the stresses, and the essential nature of the large-scale structures was unaffected by the Pressure Gradient. The wall Pressure distribution in the current experiment was designed to match the Pressure distribution on a previously studied curved-wall model where streamline curvature acted in combination with bulk compression. The addition of streamline curvature affects the turbulence strongly, although its influence on the mean velocity field is less pronounced and the modifications to the skin-friction distribution seem to follow the empirical correlations developed by Bradshaw (1974) reasonably well.
