Assessment of RANS and DES methods for realistic automotive models

Abstract This paper presents a comprehensive investigation of RANS and DES models for the Ahmed car body and a realistic automotive vehicle; the DrivAer model. A variety of RANS models, from the 1-equation Spalart Allmaras model to a low-Reynolds number Reynolds Stress model have shown an inability to consistently correctly capture the flow field for both the Ahmed car body and DrivAer model, with the under-prediction of the turbulence in the initial separated shear layer found as a key deficiency. It has been shown that the use of a hybrid RANS-LES model (in this case, Detached Eddy Simulation) offers an advantage over RANS models in terms of the force coefficients, and general flow field for both the Ahmed car body and the DrivAer model. However, for both cases even at the finest mesh level hybrid RANS-LES methods still exhibited inaccuracies. Suggestions are made on possible improvements, in particular on the use of embedded LES with synthetic turbulence generation. Finally the computational cost of each approach is compared, which shows that whilst hybrid RANS-LES offer a clear benefit over RANS models for automotive relevant flows they do so at a much increased cost.

[1]  Nikolaus A. Adams,et al.  Experimental and Numerical Investigation of the DrivAer Model , 2012 .

[2]  P. Spalart,et al.  A hybrid RANS-LES approach with delayed-DES and wall-modelled LES capabilities , 2008 .

[3]  Alistair Revell,et al.  A hybrid numerical scheme for a new formulation of delayed detached-eddy simulation (DDES) based on elliptic relaxation , 2011 .

[4]  Mesbah Uddin,et al.  Simulating DrivAer with Structured Finite Difference Overset Grids , 2015 .

[5]  P. Spalart,et al.  A New Version of Detached-eddy Simulation, Resistant to Ambiguous Grid Densities , 2006 .

[6]  Alistair Revell,et al.  Key factors in the use of DDES for the flow around a simplified car , 2015 .

[7]  Stefan Becker,et al.  Flow and Turbulence Structure in the Wake of a Simplified Car Model , 2003 .

[8]  D. Laurence,et al.  A robust k " v 2 =k elliptic blending turbulence model with improved predictions in near-wall, separated and buoyant o ws 1 , 2011 .

[9]  Sinisa Krajnovic,et al.  Large-Eddy Simulation of the Flow Around Simplified Car Model , 2004 .

[10]  Florian R. Menter,et al.  Fine-tuning of DDES and IDDES formulations to the k-ω shear stress transport model , 2013 .

[11]  Werner Haase,et al.  FLOMANIA - A European Initiative on Flow Physics Modelling , 2006 .

[12]  Emmanuel Guilmineau.  Numerical Simulations of Flow around a Realistic Generic Car Model , 2014 .

[13]  Dieter Schwamborn,et al.  ATAAC – An EU-Project Dedicated to Hybrid RANS/LES Methods , 2012 .

[14]  C. Moulinec,et al.  Optimizing Code_Saturne computations on Petascale systems , 2011 .

[15]  Domenico Caridi,et al.  Embedded Large Eddy Simulation of Flow around the Ahmed Body , 2012 .

[16]  Nikolaus A. Adams,et al.  Introduction of a New Realistic Generic Car Model for Aerodynamic Investigations , 2012 .

[17]  Remi Manceau,et al.  Computations of complex flow configurations using a modified elliptic-blending Reynolds-Stress model , 2014 .

[18]  F. Archambeau,et al.  Code Saturne: A Finite Volume Code for the computation of turbulent incompressible flows - Industrial Applications , 2004 .

[19]  B. Launder,et al.  Progress in the development of a Reynolds-stress turbulence closure , 1975, Journal of Fluid Mechanics.

[20]  A. Revell,et al.  A New Divergence Free Synthetic Eddy Method for the Reproduction of Inlet Flow Conditions for LES , 2013 .

[21]  Jochen Fröhlich,et al.  On simulating the turbulent flow around the Ahmed body: A French–German collaborative evaluation of LES and DES , 2013 .

[22]  Charles Mockett,et al.  A comprehensive study of detached-eddy simulation , 2007 .

[23]  P. Spalart,et al.  Physical and Numerical Upgrades in the Detached-Eddy Simulation of Complex Turbulent Flows , 2002 .

[24]  J. Fröhlich,et al.  Hybrid LES/RANS methods for the simulation of turbulent flows , 2008 .

[25]  Alistair Revell,et al.  Grey-Area Mitigation for the Ahmed Car Body Using Embedded DDES , 2015 .

[26]  Emmanuel Guilmineau,et al.  Numerical simulation with a DES approach for automotive flows , 2011 .

[27]  P. Spalart.  A One-Equation Turbulence Model for Aerodynamic Flows , 1992 .

[28]  C. L. Rumsey,et al.  Pressure-strain and near-wall modeling for two-dimensional separated flows By , 2012 .

[29]  Lars Davidson,et al.  LARGE EDDY SIMULATION OF THE FLOW AROUND AN AHMED BODY , 2004 .

[30]  T. Shih,et al.  A new k-ϵ eddy viscosity model for high reynolds number turbulent flows , 1995 .

[31]  E. Serre,et al.  High-order large-eddy simulation of flow over the “Ahmed body” car model , 2008 .

[32]  Gunther Ramm,et al.  Some salient features of the time - averaged ground vehicle wake , 1984 .

[33]  Werner Haase,et al.  DESider A European Effort on Hybrid RANS-LES Modelling. Notes on Numerical Fluid Mechanics and Multidisciplinary Design , 2009 .

[34]  Alistair Revell,et al.  DESider A European Effort on Hybrid RANS-LES Modelling: Results of the European-Union Funded Project, 2004 - 2007 , 2009 .

[35]  Manuel García-Villalba,et al.  Large eddy simulation of flow around the Ahmed body , 2004 .

[36]  Subrata Roy,et al.  Detached-Eddy Simulation over a Reference Ahmed Car Model , 2003 .

[37]  F. Menter.  Two-equation eddy-viscosity turbulence models for engineering applications , 1994 .

[38]  D. Cokljat,et al.  Zonal Multi-Domain Rans/Les Simulation of Airflow Over the Ahmed Body , 2005 .