Computational Study of the Aerodynamics of a Realistic Car Model by Means of RANS and Hybrid RANS/LES Approaches

The aerodynamic properties of a BMW car model, representing a 40%-scaled model of a relevant car configuration, are studied computationally by means of the Unsteady RANS (Reynolds-Averaged Navier-Stokes) and Hybrid RANS/LES (Large-Eddy Simulation) approaches. The reference database (geometry, operating parameters and surface pressure distribution) are adopted from an experimental investigation carried out in the wind tunnel of the BMW Group in Munich (Schrefl, 2008). The present computational study focuses on validation of some recently developed turbulence models for unsteady flow computations in conjunction with the universal wall treatment combining integration up to the wall and high Reynolds number wall functions in such complex flow situations. The turbulence model adopted in both Unsteady RANS and PANS (Partially-Averaged Navier Stokes) frameworks is the four-equation ζ − f formulation of Hanjalic et al. (2004) based on the Elliptic Relaxation Concept (Durbin, 1991). The latter model mimics the sub-scale model in the PANS method representing a hybrid RANS/LES strategy, proposed recently by Basara et al. (2011). Herewith a seamless transition from Unsteady RANS to the direct numerical simulation (DNS) is provided as the unresolved-to-total ratios of kinetic energy and its dissipation are varied throughout the flow domain. As a result of simulations the three-dimensional wall-pressure distribution, detailed mean flow and turbulence fields are obtained and analyzed along with experimental findings, thus enabling the study of the aerodynamic properties of this ground vehicle including also the unsteady flow phenomena in the car wake.