Scale-Resolving Simulation of an ‘On-Road’ Overtaking Maneuver Involving Model Vehicles

Aerodynamic properties of a BMW car model taking over a truck model are studied computationally by applying the scale-resolving PANS (Partially-averaged Navier-Stokes) approach. Both vehicles represent down-scaled (1:2.5), geometrically-similar models of realistic vehicle configurations for which on-road measurements have been performed by Schrefl (2008). The operating conditions of the modelled ‘on-road’ overtaking maneuver are determined by applying the dynamic similarity concept in terms of Reynolds number consistency. The simulated vehicle configuration constitutes of a non-moving truck model and a car model moving against the air flow, the velocity of which corresponds to the car velocity. The presently modelled ‘on-road’ overtaking maneuver is designed by reference to the complementary ‘quasi stationary’ event investigated experimentally in full-scale wind tunnel of the BMW Group in Munich/Ascheim by fixing the truck model at eight discrete positions relative to the car model, Schreffl (2008); accordingly, the results obtained are discussed also by reference to these measurements, in addition to the results of the realistic ‘on-road’ investigations. The turbulence modelling focus of the present work is on the validation of the PANS approach representing a variable-resolution hybrid LES/RANS modelling framework providing a smooth and seamless transition from Unsteady RANS (Reynolds-averaged Navier-Stokes) to LES (Large-eddy Simulation) in terms of a dynamic ‘resolution parameter’ variation, Basara et al. (2011). As a result of simulations detailed time-dependent mean flow and turbulence fields are obtained, thus enabling the study of the truck/car interference. The surface pressure distribution as well as the resulting drag, lift and side force and corresponding moment variations are discussed along with the available experimental database.