Transient car aerodynamics during an overtaking maneuver: a wind-tunnel flow simulation study
2022-01-1075
03/29/2022
- Event
- Content
- An overtaking process realized in a wind tunnel, implying a BMW car model passing a correspondingly designed truck model (with both vehicles being down-scaled according to 1:2.5), has been investigated computationally by applying the PANS (Partially-averaged Navier-Stokes) approach representing a scale-resolving hybrid RANS/LES (Reynolds-averaged Navier-Stokes / Large-eddy Simulation) model (Basara et al.; AIAA Journal 42(12), 2011). A complementary study including the flow past an isolated BMW car model has been preliminary performed. The characteristic car-relevant flow Reynolds number, based on the axis-center distance and air velocity (of 140 km/h) corresponds to 3 million. The present overtaking maneuver, referred to as a “quasi-stationary” sequence, has been realized by considering eight distinct positions the car model takes relative to the truck configuration. Accordingly, a complete overtaking event accounting for the car positions corresponding to the car approaching the truck, passing the truck and moving away from the truck could be reproduced. The computationally considered flow domain, meshed by 47 million polyhedral cells, coincides with experimentally investigated domain including the entire wind-tunnel plenum as well as parts of the nozzle and collector. The reference database, obtained experimentally by Schrefl (2008, PhD Thesis, TU Darmstadt, Germany, ISBN 978-3-8322-7010-0), encompasses all three aerodynamic forces – drag, lift and side forces - extracted from the three-dimensional surface pressure distribution for both the single car and the car/truck assembly for all eight characteristic positions. Accordingly, the simulation results are discussed along with the available measurements. In addition to these integral flow properties, the PANS simulations provided also the entire time-dependent mean flow and turbulence fields, thus enabling the study of the car’s aerodynamic properties under transient conditions. The results interpretation includes also the aerodynamic car response in the frequency space illustrated by means of the frequency and power density spectra applied to the side force coefficient.
- Citation
- Kutej, L., Basara, B., Tropea, C., Hussong, J. et al., "Transient car aerodynamics during an overtaking maneuver: a wind-tunnel flow simulation study," SAE Technical Paper 2022-01-1075, 2022, .