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

Abstract

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.

Turbulence Modeling Effects on the CFD Predictions of Flow over a Detailed Full-Scale Sedan Vehicle

“…A recent work by Peters et al [19], which presented higher order structured finite difference solutions using overset grids and NASA's overset grid solver Overflow, also observed similar pressure distribution differences when using the SST k − ω model. Moreover, several widely-used RANS and hybrid LES/RANS models were also applied to the DrivAer model [1,2,20,21]. It was found that RANS models were unable to predict the force coefficients correctly, especially the lift coefficient.…”

Partially-averaged Navier–Stokes simulations of two bluff body flows

“…They range from relatively simple square section infinite cylinders [26] to complete cars [27]. For a review of previous simulations, we refer to [28].…”

Tabulated Chemistry Combustion Model for Cost-Effective Numerical Simulation of Dual-Fuel Combustion Process

“…Consequently, a common practice for turbulent simulation of industrial interest is to adopt the RANS turbulence modeling approach. However, RANS models are single-point closures, relying on the assumption of self-similarity of the turbulence spectrum [17]. This assumption suggests that the complete turbulence spectrum can be defined by a single characteristic turbulent length scale.…”

“…As a result, it offers enhanced outcomes compared to the RANS method, while demanding significantly less computational resources than LES calculations. The successful implementation of the PANS technique has been demonstrated across a wide range of applications (see [17,[20][21][22]). Various PANS variants have been developed to date; for this study, a PANS model based on the k − ζ − f model proposed by Basara et al [23] is coupled with the FGM tabulated chemistry combustion model.…”