Critical assessment of some popular scale-resolving turbulence models for vehicle aerodynamics

Paper #:
  • 2017-01-1532

  • 2017-03-28
Some widely-used scale-resolving turbulence models are comparatively assessed in simulating the aerodynamic behavior of a full-scale AUDI-A1 car configuration. The presently considered hybrid RANS/LES (RANS – Reynolds-Averaged Navier-Stokes; LES – Large-Eddy Simulation) models include the well-known DES (Detached-Eddy Simulation) scheme and two variable-resolution formulations denoted by PANS (Partially-Averaged Navier-Stokes; Basara et al., AIAA J. 49(12), 2011 and Jakirlic et al., SAE Paper 2014-01-0594) and VLES (Very LES; Chang et al., Int. J. Heat and Fluid Flow 49:28-42, 2014 and Jakirlic et al., SAE Paper 2016-01-1062). Whereas the DES method represents the originally proposed formulation based on the one-equation Spalart-Almaras model (Spalart et al. 1997; 1st AFOSR Int. Conf. on DNS and LES), whose RANS/LES interface position is directly determined by the underlying grid resolution, the other two models represent ‘true’ seamless formulations, providing a smooth transition from Unsteady RANS to LES in terms of a dynamic “resolution parameter” variation. The latter parameter is evaluated by contrasting the length scale related to the residual turbulence of both PANS and VLES methods to the grid spacing. The dynamics of residual motion in both methods is modelled by a four equation k-e-z-f model (Hanjalic et al., Int. J. Heat and Fluid Flow 25:1047-1051). All computations are performed by the OpenFOAM code. The PANS and VLES formulations, in conjunction with the ‘hybrid wall functions’ used for the wall treatment, are implemented on our own. The car configuration considered accounts for mirrors, detailed underbody accommodating the exhaust system and differential gear, as well as the rotating wheels including brake discs and rim details. The solution domain representing a regular hexahedron was meshed by two grids consisting approximately of 31 and 62 millions cells in total. The results representation includes detailed time-dependent mean flow and turbulence fields, surface pressure distribution and the resulting drag, lift and side force coefficients. The discussion will be performed by contrasting the models’ predictive capabilities along with the available experimental results.
Also in:
  • SAE International Journal of Passenger Cars - Mechanical Systems - V126-6
  • SAE International Journal of Passenger Cars - Mechanical Systems - V126-6EJ
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