Grey-Area Mitigation for the Ahmed Car Body Using Embedded DDES

  • N. AshtonEmail author
  • A. Revell
  • R. Poletto
Conference paper
Part of the Notes on Numerical Fluid Mechanics and Multidisciplinary Design book series (NNFM, volume 130)


The Ahmed car body represents a generic car geometry which exhibits many of the flow features found in real-life cars despite its simplified geometry. It is a challenging test case for the turbulence modelling community as it combines both 3D separation and the formation of counter-rotating vortices, which interact together to produce a recirculation region behind the car body. It is shown that none of the RANS models tested are able to correctly predict the size of the recirculation region, regardless of modelling level, mesh resolution or the choice of the length scale (i.e. \(\omega \) or \(\varepsilon \)). All of these models under-predict the turbulence levels over the slanted back and as a consequence over-predict the separation region. The DDES simulations (regardless of the underlying URANS model) offer an improved predictive capability compared to the RANS models when the mesh resolution is sufficient. When the mesh resolution is insufficient the DDES models produces worse results than either of the URANS models. In both cases, the grey area problem is demonstrated, wherein a lack of both modelled and resolved turbulence in the initial separated shear layer results in an over-prediction of the separation region. A one-way embedded DDES approach is shown to give the best compromise between accuracy and simulation cost. It accurately predicts the level of resolved turbulence in the initial separated shear layer and thus compared to non-embedded DDES and URANS, the injection of synthetic turbulence upstream of the separation point allows for the correct level of turbulence at the onset of separation. The resulting separation zone is correctly predicted and the grey-area problem is reduced.


Recirculation Region Separation Region Mesh Resolution Reattachment Point RANS Model 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



The authors gratefully acknowledge computational support from Barcelona Supercomputer Centre (BSC) and also to the Hartree and STFC for the use of the Blue Joule Blue Gene Q machine. Part of this work was carried out under the EU project Go4Hybrid funded by the European Community in the 7th Framework Programme under Contract No. APC3-GA-2013-605361-Go4Hybrid.


  1. 1.
    Ahmed, S.R., Ramm, G., Faltin, G.: Some salient features of the time averaged ground vehicle wake. SAE-Paper 840300 (1984)Google Scholar
  2. 2.
    Archambeau, F., Mechitoua, N., Sakiz, M.: A finite volume method for the computation of turbulent incompressible flows—industrial applications. Int. J. Finite 1, 1–62 (2004)Google Scholar
  3. 3.
    Ashton, N., Prosser, R., Revell, A.: A hybrid numerical scheme for a new formulation of delayed detached-eddy simulation (DDES) based on elliptic relaxation. J. Phys. Conf. Ser. 318, 042043 (2011). doi: 10.1088/1742-6596/318/4/042043
  4. 4.
    Ashton, N., Revell, A., Prosser, R., Uribe, J.: Development of an alternative delayed detached-eddy simulation formulation based on elliptic relaxation. AIAA J. 51(2), 513–519 (2013)Google Scholar
  5. 5.
    Fournier, Y., Bonelle, J., Moulinec, C., Shang, Z., Sunderland, A., Uribe, J.: Optimizing code saturne computations on Petascale systems. Comput. Fluids 45(1), 103–108 (2011). doi: 10.1016/j.compfluid.2011.01.028
  6. 6.
    Haase, W., Aupoix, B., Bunge, U., Schwamborn, D. (eds.): FLOMANIA—A European Initiative on Flow Physics Modelling. Notes on Numerical Fluid Mechanics and Multidisciplinary Design, vol. 94. Springer, New York (2006)Google Scholar
  7. 7.
    Haase, W., Braza, M., Revell, A.: DESider—A European Effort on Hybrid RANS-LES Modelling. Notes on Numerical Fluid Mechanics and Multidisciplinary Design, vol. 103. Springer, New York (2007)Google Scholar
  8. 8.
    Jakirlić, S., Jester-Zurker, R., Tropea, C.: Report on 9th ERCOFTAC/IAHR/COST workshop on refined turbulence modelling. In: ERCOFTAC Bulletin, Darmstadt University of Technology (2002), pp. 36–43Google Scholar
  9. 9.
    Jarrin, N.: Synthetic inflow boundary conditions for the numerical simulation of turbulence. Ph.D. thesis, Manchester University (2008)Google Scholar
  10. 10.
    Krajnovic, S., Davidson, L.: Large-eddy simulation of the flow around simplified car model. In: SAE World Congress, Detroit (2004)Google Scholar
  11. 11.
    Laurence, D.L., Uribe, J.C., Utyuzhinkov, S.V.: A robust formulation of the \(\overline{v^{2}} - f\) model. Flow Turbul. Combust. 73, 169–185 (2004)Google Scholar
  12. 12.
    Lienhart, H., Becker, S.: Flow and turbulent structure in the wake of a simplified car model. SAE 01(1), 0656 (2003)Google Scholar
  13. 13.
    Manceau, R., Bonnet, J.P., Leschziner, M., Menter, F.R.: 10th Joint ERCOFTAC(SIG-15)/IAHR/QNET-CFD Workshop on Refined Flow Modelling. Universite de Poitiers (2002)Google Scholar
  14. 14.
    Manceau, R., Hanjalic, K.: Elliptic blending model: a new near-wall Reynolds-stress turbulence closure. Phys. Fluids 14, 744–754 (2001)Google Scholar
  15. 15.
    Minguez, M., Pasquetti, R., Serre, E.: High-order large-eddy simulation of flow over the Ahmed body car model. Phys. Fluids 20(9), 095,101 (2008). doi: 10.1063/1.2952595
  16. 16.
    Poletto, R., Craft, T., Revell, A.: A new divergence free synthetic eddy method for the reproduction of inlet flow conditions for LES. Flow Turbul. Combust. 519–539 (2013). doi: 10.1007/s10494-013-9488-2
  17. 17.
    Serre, E., Minguez, M., Pasquetti, R., Guilmineau, E., Deng, G.B., Kornhaas, M., Schäfer, M., Fröhlich, J., Hinterberger, C., Rodi, W.: On simulating the turbulent flow around the Ahmed body: a FrenchGerman collaborative evaluation of LES and DES. Comput. Fluids 78, 10–23 (2013). doi: 10.1016/j.compfluid.2011.05.017
  18. 18.
    Spalart, P.R., Deck, S., Shur, M.L., Squires, K.D., Strelets, M.K., Travin, A.: A new version of detached-eddy simulation, resistant to ambiguous grid densities. Theor. Comput. Fluid Dynam. 20(3), 181–195 (2006). doi: 10.1007/s00162-006-0015-0
  19. 19.
    Spalart, P.R., Jou, W.H., Strelets, M., Allmaras, S.R.: Comments on the feasibility of LES for wings and on a hybrid, RANS/ES approach. In: Advances in DNS/LES, Proceedings of 1st AFOSR International Conference on DNS/LES 1, 137–147 (1997)Google Scholar
  20. 20.
    Travin, A., Shur, M., Strelets, M., Spalart, P.R.: Detached-eddy simulations past a circular cylinder. Flow Turbul. Combust. 63, 293–313 (2000)Google Scholar

Copyright information

© Springer International Publishing Switzerland 2015

Authors and Affiliations

  1. 1.School of Mechanical, Aerospace & Civil EngineeringUniversity of ManchesterManchesterUK

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