Christophe Brun - Academia.edu (original) (raw)
Papers by Christophe Brun
Large eddy simulation of the turbulent flow which spatially develops in a plane channel with a le... more Large eddy simulation of the turbulent flow which spatially develops in a plane channel with a length of 88h will be presented for Re=4880 and M=0.7. The effect of realistic inflow conditions and low reflective outflow conditions will be analysed and discussed. Supersonic channel flow case and distorsion of the flow by mean of adverse pressure gradient will be further considered.
La modélisation de la turbulence est un élément essentiel de la prédiction de la qualité de l'... more La modélisation de la turbulence est un élément essentiel de la prédiction de la qualité de l'air en vallée alpine, en particulier en situation stablement stratifiée. Des SGE à haute résolution sont effectuées avec le code de calcul Meso-NH. On évalue l'effet des conditions aux limites, refroidissement et rugosité en paroi, sur le comportement turbulent de l'écoulement catabatique généré le long d'une pente modèle. La prise en compte du transport et du mélange de scalaire est envisagée.
L'étude consiste à appliquer la méthode de Simulation des Grandes Echelles de la turbulence a... more L'étude consiste à appliquer la méthode de Simulation des Grandes Echelles de la turbulence afin de caractériser l'effet d'un gradient de pression adverse en paroi sur le décollement d'un écoulement compressible. L'effet de gradient de pression adverse est artificiellement modélisé par une distribution de force en proche paroi. Les résultats sont analysée à la fois sur le plan statistique de la turbulence et en terme de phénoménologie des structures cohérentes développées et des lois de paroi pour les couches limites compressibles décollées sont proposées.
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2009
The near wall behaviour of complex turbulent flows is investigated by dimensional considerations ... more The near wall behaviour of complex turbulent flows is investigated by dimensional considerations and a priori investigations. We consider separated incompressible and compressible flows. In incompressible turbulent flows, it is found that the flow in the immediate vicinity of the wall is dependent on two parameters, based on wall friction and local pressure gradient, respectively. In compressible turbulent flows, a
ESAIM: Proceedings, 2007
The paper presents near-wall scaling in incompressible and compressible flows. It concentrates on... more The paper presents near-wall scaling in incompressible and compressible flows. It concentrates on flows with streamwise pressure gradients which render traditional scaling inapplicable. For incompressible flows a scaling for the velocity profiles is introduced based on both the friction velocity and the pressure gradient. For compressible flows a scaling is developed for the velocity and the temperature. This scaling is based on wall friction, pressure gradient and wall heat flux. We define two new parameters α and β where α defines a measure for the ratio between wall friction and pressure gradient and β defines the ratio between wall heat flux and pressure gradient. For zero pressure gradient flows the traditional scaling is recovered. A priori tests are performed by means of Direct Numerical Simulations (DNS). The compressible scaling is analyzed on channel flow with non-adiabatic walls and adverse pressure gradient. The incompressible scaling is analyzed on channel flow with periodic hill constrictions. Finally a wall model based on the new scaling is tested a posteriori by means of Large Eddy Simulation (LES).
Fluid Mechanics and Its Applications, 2002
We propose a new mixed model for Large Eddy-Simulation based on the 3D spatial velocity increment... more We propose a new mixed model for Large Eddy-Simulation based on the 3D spatial velocity increment. This approach blends the non-linear properties of the Increment model (Brun & Friedrich (2001)) with the eddy viscosity characteristics of the Structure Function model (Métais & Lesieur (1992)). The behaviour of this subgrid scale model is studied both via a priori tests of a plane jet at ReH=3000 and Large Eddy-Simulation of a round jet at ReD=25000. This approach allows to describe both forward and backward energy transfer encountered in transitional shear flows.
The Cryosphere, 2014
ABSTRACT A total of 3 years of blowing-snow observations and associated meteorology along a 7 m m... more ABSTRACT A total of 3 years of blowing-snow observations and associated meteorology along a 7 m mast at site D17 in coastal Adelie Land are presented. The observations are used to address three atmospheric-moisture issues related to the occurrence of blowing snow, a feature which largely affects many regions of Antarctica: ( 1) blowing-snow sublimation raises the moisture content of the surface atmosphere close to saturation, and atmospheric models and meteorological analyses that do not carry blowing-snow parameterizations are affected by a systematic dry bias; ( 2) while snowpack modelling with a parameterization of surface-snow erosion by wind can reproduce the variability of snow accumulation and ablation, ignoring the high levels of atmospheric-moisture content associated with blowing snow results in overestimating surface sublimation, affecting the energy budget of the snowpack; ( 3) the well-known profile method of calculating turbulent moisture fluxes is not applicable when blowing snow occurs, because moisture gradients are weak due to blowing-snow sublimation, and the impact of measurement uncertainties are strongly amplified in the case of strong winds.
The Cryosphere Discussions, 2014
ABSTRACT Dome C on the Antarctic plateau (75°06' S, 123°20' E, 3233 m a.s.l.) was... more ABSTRACT Dome C on the Antarctic plateau (75°06' S, 123°20' E, 3233 m a.s.l.) was selected as one of the 119 CF-sites for the CMIP5/IPCC intercomparison project. For these sites, the participating climate modeling groups have been asked to produce a special set of high frequency diagnostics. Dome C has been selected because of the extreme weather and climate of the Antarctic plateau, but also because of the year-long continuous observations, performed with support from the permanent French-Italian Concordia station. The lower atmospheric boundary layer at Dome C is monitored since January 2008 (Genthon et al., J. Geophys. Res., 2010). Anemometers, thermometers and hygrometers were deployed at 6 levels above the surface up to ~42 m. Harsh local conditions (extreme cold temperatures, frost deposition) have affected the operation of the instruments. Several failed during winter 2008 but improvements have allowed almost continuous records with only limited interruptions since 2009. Cases of thermal convective mixing (adiabatic temperature profile, in summer) as well as cases of very strong inversions (more than 2°C per meter locally, in winter) were recorded. In 2010, the temperature at the lowest level dropped below -80°C, whereas in 2009 the minimal temperature is 10 degrees higher. Winter 2009, milder but twice as much windswept than the next winter, is remarkable for the occurrences of extreme "warm events" : for two days, the temperature approached the -30°C in the depths of winter. Independently, the Antarctic Meteorological Research Center automatic weather station at Dome C indicates that these two winters are the warmest and coldest on record over the past decade. Therefore, it may be supposed that the 2009-2010 time series together contain enough variability to be used for the evaluation of climate models. The data have been compared with the ECMWF meteorological analyzes, and with AMIP simulations of CMIP5 models. The coarse vertical resolution of general circulation models limits the degree of details of the comparison. Nevertheless, this is sufficient to reveal that many of the observations' features can be reproduced, including large inter-annual variability, extreme winter inversions, warm events, etc. However, it is clear that many models fail to account for the most extreme characteristics of the boundary layer on the Antarctic plateau, including the extreme temperature's values and the duration and intensity of warm events. While all models predict significant warming over Antarctica the details of this warming and impact on the general meteorology of the Antarctic plateau (including e.g. snowfall) may be questioned.
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2009
... Jacques Boree..... 253 Wall Scaling and Wall Models for Complex Turbulent Flows Michael Manha... more ... Jacques Boree..... 253 Wall Scaling and Wall Models for Complex Turbulent Flows Michael Manhart, Nikolaus Peller, Margareta Petrovan Boiarciuc, Christophe Brun..... 283 High-Order ...
Theoretical and Computational Fluid Dynamics, 2008
A new extended inner scaling is proposed for the wall layer of wall-bounded flows under the influ... more A new extended inner scaling is proposed for the wall layer of wall-bounded flows under the influence of both wall shear stress and streamwise pressure gradient. This scaling avoids problems of the classical wall coordinates close to flow separation and reattachment. Based on the proposed extended velocity and length scales a universal nondimensional family of velocity profiles is derived for the viscous region in the vicinity of a wall that depend on wall distance and a parameter α quantifying the importance of the streamwise pressure gradient with respect to the wall shear stress in the momentum balance. The performance of the proposed extended scaling is investigated in two different flow fields, a separating and reattaching turbulent boundary layer and a turbulent flow over a periodic arrangement of smoothly contoured hills. Both flows are results of highly resolved direct numerical simulation (DNS). The results show that the viscous assumptions are valid up to about two extended wall units. If the profiles are scaled by the extended inner coordinates, they seem to behave in a universal way. This gives rise to the hope that a universal behavior of velocity profiles can be found in the proposed extended inner coordinates even beyond the validity of the extended viscous law of the wall.
Theoretical and Computational Fluid Dynamics, 2008
The present study is a contribution to the analysis of wall-bounded compressible flows, including... more The present study is a contribution to the analysis of wall-bounded compressible flows, including a special focus on wall modeling for compressible turbulent boundary layer in a plane channel. large eddy simulation (LES) of fully developed isothermal channel flows at Re = 3, 000 and Re = 4, 880 with a sufficient mesh refinement at the wall are carried out in the Mach number range 0.3 ≤ M ≤ 3 for two different source term formulations: first the classical extension of the incompressible configuration by Coleman et al. (J. Fluid Mech. 305:159-183, 1995), second a formulation presently derived to model both streamwise pressure drop and streamwise internal energy loss in a spatially developed compressible channel flow. It is shown that the second formulation is consistent with the spatial problem and yields a much stronger cooling effect at the wall than the classical formulation. Based on the present LES data bank, compressibility and low Reynolds number effects are analysed in terms of coherent structure and statistics. A study of the universality of the structure of the turbulence in non-hypersonic compressible boundary layers (M ≤ 5) is performed in reference to Bradshaw (Annu. Rev. Fluid. Mech. 9:33-54, 1977). An improvement of the van Driest transformation is proposed; it accounts for both density and viscosity changes in the wall layer. Consistently, a new integral wall scaling (y c+ ) which accounts for strong temperature gradients at the wall is developed for the present non-adiabatic compressible flow. The modification of the strong Reynolds analogy proposed by Huang et al. (J. Fluid Mech. 305:185-218, 1995) to model the correlation between velocity and temperature for nonadiabatic wall layers is assessed on the basis of a Crocco-Busemann relation specific to channel flow. The key role of the mixing turbulent Prandtl number Pr m is pointed out. Results show very good agreement for both source formulations although each of them involve a very different amount of energy transfer at the wall.
Theoretical and Computational Fluid Dynamics, 2006
A new subgrid scale (SGS) modelling concept for large-eddy simulation (LES) of incompressible flo... more A new subgrid scale (SGS) modelling concept for large-eddy simulation (LES) of incompressible flow is proposed based on the three-dimensional spatial velocity increment δu i . The new model is inspired by the structure function formulation developed by Métais and Lesieur and applied in the context of the scale similarity type formulation. First, the similarity between the SGS stress tensor τ i j and the velocity increment tensor Q i j = δu i δu j is analyzed analytically and numerically using a priori tests of fully developed pipe flow at Re τ = 180. Both forward and backward energy transfers between resolved and unresolved scales of the flow are well predicted with a SGS model based on Q i j . Secondly, a posteriori tests are performed for two families of turbulent shear flows. LES of fully developed pipe flow up to Re τ = 520 and LES of round turbulent jet at Re D = 25000 carried out with a dynamic version of the model provide promising results that confirm the power of this approach for wall-bounded and free shear flows.
Physics of Fluids, 2001
ABSTRACT Based on Taylor series expansions for the filtered velocity field, we present an analyti... more ABSTRACT Based on Taylor series expansions for the filtered velocity field, we present an analytical study of the “Germano identity” used in the dynamic sub-grid scale (SGS) model for large eddy simulation (LES). We consider the case of explicit filtering defined in physical space and show that the choice of the length scale which characterizes the test SGS tensor Tij is a main issue in modeling the “Germano identity.” In the field of eddy-viscosity models, we demonstrate the accuracy of a Gaussian formulation lfg2 = lf2+lg2, based on a priori tests of fully developed pipe flow. More than a generalization of formal results [B. Vreman, B. Geurts, and H. Kuerten, J. Fluid Mech. 339, 357 (1997)], our study reveals constraints and limitations of the dynamic approach.
Physics of Fluids, 2008
The spectral eddy-viscosity and eddy-diffusivity closures derived from the Eddy-Damped Qusasi-Nor... more The spectral eddy-viscosity and eddy-diffusivity closures derived from the Eddy-Damped Qusasi-Normal Markovian theory, and one of its physical space counterparts, i.e., the structure function model ͓Métais and Lesieur, J. Fluid Mech. 239, 157 ͑1992͔͒, are revisited to account for molecular viscosity and diffusivity effects. The subgrid-scale Schmidt number ͑usually set to Sc t Ϸ 0.6͒ is analytically derived from the Eddy-Damped Qusasi-Normal Markovian theory and shown to be Reynolds number dependent, a property of utmost importance for flows involving scalar transport at moderate Reynolds numbers or during the transition to turbulence. A priori tests in direct numerical simulation of homogeneous isotropic turbulence ͓da Silva and Pereira, Phys. Fluids 19, 1 ͑2007͔͒ and in spatially evolving turbulent plane jets ͓da Silva and Métais, J. Fluid Mech. 473, 103 ͑2002͔͒, as well as a posteriori ͑large eddy simulation͒ tests in a round jet are carried out and show that the present viscous structure function model improves the results from the classical approaches and at a comparatively small computational cost.
Journal of Applied Sciences, 2009
ABSTRACT The effect of Reynolds number and inlet flow conditions on the topological structures of... more ABSTRACT The effect of Reynolds number and inlet flow conditions on the topological structures of an incompressible jet in crossflow (JICF) with a passive scalar is investigated numerically using large-eddy simulation. The study is focused on two Reynolds number values of 2,000 and 20,000 and two kinds of inlet conditions, namely a randomly perturbed top-hat velocity profile and a fully developed turbulent inflow issuing from a temporally-evolving duct. The jet to crossflow velocity ratio is 10. A passive scalar is also seeded in the jet. The flow configuration is a model of an experimental study performed at the CEA-Grenoble [1].
International Journal of Heat and Fluid Flow, 2011
A coupled experimental/numerical analysis of turbulent flow past a square cylinder is performed a... more A coupled experimental/numerical analysis of turbulent flow past a square cylinder is performed at the ERCOFTAC Reynolds number Re=U∞D/ν=21,400, where U∞ is the inflow velocity and D the cylinder height. Complementary Laser Doppler Velocimetry (LDV) and high-order large-eddy simulations (LES) approaches, based on a spectral vanishing technique (SVV-LES), provide a comprehensive data base including both instantaneous data and post-processed statistics.
Flow, Turbulence and Combustion, 2008
The purpose of the present work is to study the various specific time scales of the turbulent sep... more The purpose of the present work is to study the various specific time scales of the turbulent separating flow around a square cylinder, in order to determine the Reynolds number effect on the separating shear layer, where occurs a transition to turbulence. Unsteady analysis based on large eddy simulation (LES) at intermediate Reynolds numbers and laser doppler velocimetry (LDV) measurements at high Reynolds numbers are carried out. The Reynolds number, based on the cylinder diameter D and the inflow velocity U o , is ranging from Re = 50 to Re = 300,000. A special focus is performed on the coherent structures developing on the sides and in the wake of a square cylinder. For a large Reynolds number range above Re ≈ 1,000, both signatures of Von Karman (VK) and Kelvin–Helmholtz (KH) type vortical structures are found on velocity time samples. The combination of their frequency signature is studied based on Fourier and wavelet analysis. In the present study, We observe the occurrence of KH pairings in the separating shear layer on the side of the cylinder, and confirm the intermittency nature of such a shear flow. These issues concerning the structure of the near wake shear layer which were addressed for the round cylinder case in a recent experimental publication (Rajagopalan and Antonia, Exp Fluids 38:393–402, 2005) are of interest in the present flow configuration as well.
Experiments in Fluids, 2004
Wakes, and their interaction behind two parallel cylinders lying in a plane perpendicular to the ... more Wakes, and their interaction behind two parallel cylinders lying in a plane perpendicular to the flow, have been investigated experimentally in the sub-critical Reynolds number regime. The experiments were performed in a water channel using laser Doppler velocimetry. The gap between the two cylinders was less than the cylinder diameter, a geometry referred to as strong interaction configuration. In this case the blockage is strong and a gap-jet appears between the cylinders. Two flow regimes of the near wake region have been identified: one below a critical Reynolds number Re c 2]1000;1700[, where the gap jet is stably deflected to one side and the double near-wake becomes asymmetric; the other, above Re c , where the gap-jet deflection is unstable and a random flopping phenomenon takes place. When Re<Re c , two different Strouhal numbers are identified, related to the Kármán vortex shedding behind each cylinder. When Re>Re c , a third frequency appears in the near wake, related to the development of Kelvin-Helmholtz vortices in the separated shear layer of the cylinders [Prasad A, Williamson CHK (1997) J Fluid Mech 333:375]. The observed flopping behavior is attributed to the birth of these Kelvin-Helmholtz instabilities and their intermittent nature. Further downstream, beyond about five cylinder diameters, the random flopping flow phenomena disappear while a slightly asymmetric single wake persists. It is characterized by a Strouhal number St=0.13, a value that one would normally measure behind a single cylinder of twice its diameter.
Large eddy simulation of the turbulent flow which spatially develops in a plane channel with a le... more Large eddy simulation of the turbulent flow which spatially develops in a plane channel with a length of 88h will be presented for Re=4880 and M=0.7. The effect of realistic inflow conditions and low reflective outflow conditions will be analysed and discussed. Supersonic channel flow case and distorsion of the flow by mean of adverse pressure gradient will be further considered.
La modélisation de la turbulence est un élément essentiel de la prédiction de la qualité de l'... more La modélisation de la turbulence est un élément essentiel de la prédiction de la qualité de l'air en vallée alpine, en particulier en situation stablement stratifiée. Des SGE à haute résolution sont effectuées avec le code de calcul Meso-NH. On évalue l'effet des conditions aux limites, refroidissement et rugosité en paroi, sur le comportement turbulent de l'écoulement catabatique généré le long d'une pente modèle. La prise en compte du transport et du mélange de scalaire est envisagée.
L'étude consiste à appliquer la méthode de Simulation des Grandes Echelles de la turbulence a... more L'étude consiste à appliquer la méthode de Simulation des Grandes Echelles de la turbulence afin de caractériser l'effet d'un gradient de pression adverse en paroi sur le décollement d'un écoulement compressible. L'effet de gradient de pression adverse est artificiellement modélisé par une distribution de force en proche paroi. Les résultats sont analysée à la fois sur le plan statistique de la turbulence et en terme de phénoménologie des structures cohérentes développées et des lois de paroi pour les couches limites compressibles décollées sont proposées.
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2009
The near wall behaviour of complex turbulent flows is investigated by dimensional considerations ... more The near wall behaviour of complex turbulent flows is investigated by dimensional considerations and a priori investigations. We consider separated incompressible and compressible flows. In incompressible turbulent flows, it is found that the flow in the immediate vicinity of the wall is dependent on two parameters, based on wall friction and local pressure gradient, respectively. In compressible turbulent flows, a
ESAIM: Proceedings, 2007
The paper presents near-wall scaling in incompressible and compressible flows. It concentrates on... more The paper presents near-wall scaling in incompressible and compressible flows. It concentrates on flows with streamwise pressure gradients which render traditional scaling inapplicable. For incompressible flows a scaling for the velocity profiles is introduced based on both the friction velocity and the pressure gradient. For compressible flows a scaling is developed for the velocity and the temperature. This scaling is based on wall friction, pressure gradient and wall heat flux. We define two new parameters α and β where α defines a measure for the ratio between wall friction and pressure gradient and β defines the ratio between wall heat flux and pressure gradient. For zero pressure gradient flows the traditional scaling is recovered. A priori tests are performed by means of Direct Numerical Simulations (DNS). The compressible scaling is analyzed on channel flow with non-adiabatic walls and adverse pressure gradient. The incompressible scaling is analyzed on channel flow with periodic hill constrictions. Finally a wall model based on the new scaling is tested a posteriori by means of Large Eddy Simulation (LES).
Fluid Mechanics and Its Applications, 2002
We propose a new mixed model for Large Eddy-Simulation based on the 3D spatial velocity increment... more We propose a new mixed model for Large Eddy-Simulation based on the 3D spatial velocity increment. This approach blends the non-linear properties of the Increment model (Brun & Friedrich (2001)) with the eddy viscosity characteristics of the Structure Function model (Métais & Lesieur (1992)). The behaviour of this subgrid scale model is studied both via a priori tests of a plane jet at ReH=3000 and Large Eddy-Simulation of a round jet at ReD=25000. This approach allows to describe both forward and backward energy transfer encountered in transitional shear flows.
The Cryosphere, 2014
ABSTRACT A total of 3 years of blowing-snow observations and associated meteorology along a 7 m m... more ABSTRACT A total of 3 years of blowing-snow observations and associated meteorology along a 7 m mast at site D17 in coastal Adelie Land are presented. The observations are used to address three atmospheric-moisture issues related to the occurrence of blowing snow, a feature which largely affects many regions of Antarctica: ( 1) blowing-snow sublimation raises the moisture content of the surface atmosphere close to saturation, and atmospheric models and meteorological analyses that do not carry blowing-snow parameterizations are affected by a systematic dry bias; ( 2) while snowpack modelling with a parameterization of surface-snow erosion by wind can reproduce the variability of snow accumulation and ablation, ignoring the high levels of atmospheric-moisture content associated with blowing snow results in overestimating surface sublimation, affecting the energy budget of the snowpack; ( 3) the well-known profile method of calculating turbulent moisture fluxes is not applicable when blowing snow occurs, because moisture gradients are weak due to blowing-snow sublimation, and the impact of measurement uncertainties are strongly amplified in the case of strong winds.
The Cryosphere Discussions, 2014
ABSTRACT Dome C on the Antarctic plateau (75°06' S, 123°20' E, 3233 m a.s.l.) was... more ABSTRACT Dome C on the Antarctic plateau (75°06' S, 123°20' E, 3233 m a.s.l.) was selected as one of the 119 CF-sites for the CMIP5/IPCC intercomparison project. For these sites, the participating climate modeling groups have been asked to produce a special set of high frequency diagnostics. Dome C has been selected because of the extreme weather and climate of the Antarctic plateau, but also because of the year-long continuous observations, performed with support from the permanent French-Italian Concordia station. The lower atmospheric boundary layer at Dome C is monitored since January 2008 (Genthon et al., J. Geophys. Res., 2010). Anemometers, thermometers and hygrometers were deployed at 6 levels above the surface up to ~42 m. Harsh local conditions (extreme cold temperatures, frost deposition) have affected the operation of the instruments. Several failed during winter 2008 but improvements have allowed almost continuous records with only limited interruptions since 2009. Cases of thermal convective mixing (adiabatic temperature profile, in summer) as well as cases of very strong inversions (more than 2°C per meter locally, in winter) were recorded. In 2010, the temperature at the lowest level dropped below -80°C, whereas in 2009 the minimal temperature is 10 degrees higher. Winter 2009, milder but twice as much windswept than the next winter, is remarkable for the occurrences of extreme "warm events" : for two days, the temperature approached the -30°C in the depths of winter. Independently, the Antarctic Meteorological Research Center automatic weather station at Dome C indicates that these two winters are the warmest and coldest on record over the past decade. Therefore, it may be supposed that the 2009-2010 time series together contain enough variability to be used for the evaluation of climate models. The data have been compared with the ECMWF meteorological analyzes, and with AMIP simulations of CMIP5 models. The coarse vertical resolution of general circulation models limits the degree of details of the comparison. Nevertheless, this is sufficient to reveal that many of the observations' features can be reproduced, including large inter-annual variability, extreme winter inversions, warm events, etc. However, it is clear that many models fail to account for the most extreme characteristics of the boundary layer on the Antarctic plateau, including the extreme temperature's values and the duration and intensity of warm events. While all models predict significant warming over Antarctica the details of this warming and impact on the general meteorology of the Antarctic plateau (including e.g. snowfall) may be questioned.
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2009
... Jacques Boree..... 253 Wall Scaling and Wall Models for Complex Turbulent Flows Michael Manha... more ... Jacques Boree..... 253 Wall Scaling and Wall Models for Complex Turbulent Flows Michael Manhart, Nikolaus Peller, Margareta Petrovan Boiarciuc, Christophe Brun..... 283 High-Order ...
Theoretical and Computational Fluid Dynamics, 2008
A new extended inner scaling is proposed for the wall layer of wall-bounded flows under the influ... more A new extended inner scaling is proposed for the wall layer of wall-bounded flows under the influence of both wall shear stress and streamwise pressure gradient. This scaling avoids problems of the classical wall coordinates close to flow separation and reattachment. Based on the proposed extended velocity and length scales a universal nondimensional family of velocity profiles is derived for the viscous region in the vicinity of a wall that depend on wall distance and a parameter α quantifying the importance of the streamwise pressure gradient with respect to the wall shear stress in the momentum balance. The performance of the proposed extended scaling is investigated in two different flow fields, a separating and reattaching turbulent boundary layer and a turbulent flow over a periodic arrangement of smoothly contoured hills. Both flows are results of highly resolved direct numerical simulation (DNS). The results show that the viscous assumptions are valid up to about two extended wall units. If the profiles are scaled by the extended inner coordinates, they seem to behave in a universal way. This gives rise to the hope that a universal behavior of velocity profiles can be found in the proposed extended inner coordinates even beyond the validity of the extended viscous law of the wall.
Theoretical and Computational Fluid Dynamics, 2008
The present study is a contribution to the analysis of wall-bounded compressible flows, including... more The present study is a contribution to the analysis of wall-bounded compressible flows, including a special focus on wall modeling for compressible turbulent boundary layer in a plane channel. large eddy simulation (LES) of fully developed isothermal channel flows at Re = 3, 000 and Re = 4, 880 with a sufficient mesh refinement at the wall are carried out in the Mach number range 0.3 ≤ M ≤ 3 for two different source term formulations: first the classical extension of the incompressible configuration by Coleman et al. (J. Fluid Mech. 305:159-183, 1995), second a formulation presently derived to model both streamwise pressure drop and streamwise internal energy loss in a spatially developed compressible channel flow. It is shown that the second formulation is consistent with the spatial problem and yields a much stronger cooling effect at the wall than the classical formulation. Based on the present LES data bank, compressibility and low Reynolds number effects are analysed in terms of coherent structure and statistics. A study of the universality of the structure of the turbulence in non-hypersonic compressible boundary layers (M ≤ 5) is performed in reference to Bradshaw (Annu. Rev. Fluid. Mech. 9:33-54, 1977). An improvement of the van Driest transformation is proposed; it accounts for both density and viscosity changes in the wall layer. Consistently, a new integral wall scaling (y c+ ) which accounts for strong temperature gradients at the wall is developed for the present non-adiabatic compressible flow. The modification of the strong Reynolds analogy proposed by Huang et al. (J. Fluid Mech. 305:185-218, 1995) to model the correlation between velocity and temperature for nonadiabatic wall layers is assessed on the basis of a Crocco-Busemann relation specific to channel flow. The key role of the mixing turbulent Prandtl number Pr m is pointed out. Results show very good agreement for both source formulations although each of them involve a very different amount of energy transfer at the wall.
Theoretical and Computational Fluid Dynamics, 2006
A new subgrid scale (SGS) modelling concept for large-eddy simulation (LES) of incompressible flo... more A new subgrid scale (SGS) modelling concept for large-eddy simulation (LES) of incompressible flow is proposed based on the three-dimensional spatial velocity increment δu i . The new model is inspired by the structure function formulation developed by Métais and Lesieur and applied in the context of the scale similarity type formulation. First, the similarity between the SGS stress tensor τ i j and the velocity increment tensor Q i j = δu i δu j is analyzed analytically and numerically using a priori tests of fully developed pipe flow at Re τ = 180. Both forward and backward energy transfers between resolved and unresolved scales of the flow are well predicted with a SGS model based on Q i j . Secondly, a posteriori tests are performed for two families of turbulent shear flows. LES of fully developed pipe flow up to Re τ = 520 and LES of round turbulent jet at Re D = 25000 carried out with a dynamic version of the model provide promising results that confirm the power of this approach for wall-bounded and free shear flows.
Physics of Fluids, 2001
ABSTRACT Based on Taylor series expansions for the filtered velocity field, we present an analyti... more ABSTRACT Based on Taylor series expansions for the filtered velocity field, we present an analytical study of the “Germano identity” used in the dynamic sub-grid scale (SGS) model for large eddy simulation (LES). We consider the case of explicit filtering defined in physical space and show that the choice of the length scale which characterizes the test SGS tensor Tij is a main issue in modeling the “Germano identity.” In the field of eddy-viscosity models, we demonstrate the accuracy of a Gaussian formulation lfg2 = lf2+lg2, based on a priori tests of fully developed pipe flow. More than a generalization of formal results [B. Vreman, B. Geurts, and H. Kuerten, J. Fluid Mech. 339, 357 (1997)], our study reveals constraints and limitations of the dynamic approach.
Physics of Fluids, 2008
The spectral eddy-viscosity and eddy-diffusivity closures derived from the Eddy-Damped Qusasi-Nor... more The spectral eddy-viscosity and eddy-diffusivity closures derived from the Eddy-Damped Qusasi-Normal Markovian theory, and one of its physical space counterparts, i.e., the structure function model ͓Métais and Lesieur, J. Fluid Mech. 239, 157 ͑1992͔͒, are revisited to account for molecular viscosity and diffusivity effects. The subgrid-scale Schmidt number ͑usually set to Sc t Ϸ 0.6͒ is analytically derived from the Eddy-Damped Qusasi-Normal Markovian theory and shown to be Reynolds number dependent, a property of utmost importance for flows involving scalar transport at moderate Reynolds numbers or during the transition to turbulence. A priori tests in direct numerical simulation of homogeneous isotropic turbulence ͓da Silva and Pereira, Phys. Fluids 19, 1 ͑2007͔͒ and in spatially evolving turbulent plane jets ͓da Silva and Métais, J. Fluid Mech. 473, 103 ͑2002͔͒, as well as a posteriori ͑large eddy simulation͒ tests in a round jet are carried out and show that the present viscous structure function model improves the results from the classical approaches and at a comparatively small computational cost.
Journal of Applied Sciences, 2009
ABSTRACT The effect of Reynolds number and inlet flow conditions on the topological structures of... more ABSTRACT The effect of Reynolds number and inlet flow conditions on the topological structures of an incompressible jet in crossflow (JICF) with a passive scalar is investigated numerically using large-eddy simulation. The study is focused on two Reynolds number values of 2,000 and 20,000 and two kinds of inlet conditions, namely a randomly perturbed top-hat velocity profile and a fully developed turbulent inflow issuing from a temporally-evolving duct. The jet to crossflow velocity ratio is 10. A passive scalar is also seeded in the jet. The flow configuration is a model of an experimental study performed at the CEA-Grenoble [1].
International Journal of Heat and Fluid Flow, 2011
A coupled experimental/numerical analysis of turbulent flow past a square cylinder is performed a... more A coupled experimental/numerical analysis of turbulent flow past a square cylinder is performed at the ERCOFTAC Reynolds number Re=U∞D/ν=21,400, where U∞ is the inflow velocity and D the cylinder height. Complementary Laser Doppler Velocimetry (LDV) and high-order large-eddy simulations (LES) approaches, based on a spectral vanishing technique (SVV-LES), provide a comprehensive data base including both instantaneous data and post-processed statistics.
Flow, Turbulence and Combustion, 2008
The purpose of the present work is to study the various specific time scales of the turbulent sep... more The purpose of the present work is to study the various specific time scales of the turbulent separating flow around a square cylinder, in order to determine the Reynolds number effect on the separating shear layer, where occurs a transition to turbulence. Unsteady analysis based on large eddy simulation (LES) at intermediate Reynolds numbers and laser doppler velocimetry (LDV) measurements at high Reynolds numbers are carried out. The Reynolds number, based on the cylinder diameter D and the inflow velocity U o , is ranging from Re = 50 to Re = 300,000. A special focus is performed on the coherent structures developing on the sides and in the wake of a square cylinder. For a large Reynolds number range above Re ≈ 1,000, both signatures of Von Karman (VK) and Kelvin–Helmholtz (KH) type vortical structures are found on velocity time samples. The combination of their frequency signature is studied based on Fourier and wavelet analysis. In the present study, We observe the occurrence of KH pairings in the separating shear layer on the side of the cylinder, and confirm the intermittency nature of such a shear flow. These issues concerning the structure of the near wake shear layer which were addressed for the round cylinder case in a recent experimental publication (Rajagopalan and Antonia, Exp Fluids 38:393–402, 2005) are of interest in the present flow configuration as well.
Experiments in Fluids, 2004
Wakes, and their interaction behind two parallel cylinders lying in a plane perpendicular to the ... more Wakes, and their interaction behind two parallel cylinders lying in a plane perpendicular to the flow, have been investigated experimentally in the sub-critical Reynolds number regime. The experiments were performed in a water channel using laser Doppler velocimetry. The gap between the two cylinders was less than the cylinder diameter, a geometry referred to as strong interaction configuration. In this case the blockage is strong and a gap-jet appears between the cylinders. Two flow regimes of the near wake region have been identified: one below a critical Reynolds number Re c 2]1000;1700[, where the gap jet is stably deflected to one side and the double near-wake becomes asymmetric; the other, above Re c , where the gap-jet deflection is unstable and a random flopping phenomenon takes place. When Re<Re c , two different Strouhal numbers are identified, related to the Kármán vortex shedding behind each cylinder. When Re>Re c , a third frequency appears in the near wake, related to the development of Kelvin-Helmholtz vortices in the separated shear layer of the cylinders [Prasad A, Williamson CHK (1997) J Fluid Mech 333:375]. The observed flopping behavior is attributed to the birth of these Kelvin-Helmholtz instabilities and their intermittent nature. Further downstream, beyond about five cylinder diameters, the random flopping flow phenomena disappear while a slightly asymmetric single wake persists. It is characterized by a Strouhal number St=0.13, a value that one would normally measure behind a single cylinder of twice its diameter.