Experiments and Calculations Relevant to Aerodynamic Effects during Highway Passing Maneuvers

Aerodynamic effects during highway passing maneuvers are still not well documented. To better understand these effects, a 40% car-truck overtaking process has been carried out in the BMW wind tunnel. As a first step, the car aerodynamics has been measured without the truck to establish the reference pressure distribution for subsequent tests. The overtaking process has been approximated by fixing the truck model at eight stationary positions relative to the car model. This approximates the overtaking process as a quasi-stationary process. The reference calculations are performed with a new variant of ¯v2- f model, the so-called ζ-f model (Hanjalic et al., 2004). Furthermore, the calculations are also performed by using recently proposed Partially-averaged Navier Stokes (PANS) model (Girimaji et al., 2003, Girimaji and Hamid, 2005) in order to capture unsteady effects more correctly compared with the unsteady RANS. Because of its extensive reference database, the well-known Ahmed body benchmark (25 degrees) was computationally investigated as an introductory case with respect to the comparative assessment of the RANS and PANS approaches. A validation procedure for the PANS method is then conducted by computing the single passenger car (40% BMW model).