The Application of a One-Way Coupled Aerodynamic and Multi-Body Dynamics Simulation Process to Predict Vehicle Response during a Severe Crosswind Event

Industry trends towards lighter, more aerodynamically efficient road vehicles have the potential to degrade a vehicle’s response to crosswinds. In this paper, a methodology is outlined that indirectly couples a computational fluid dynamics (CFD) simulation of the vehicle’s aerodynamic characteristics with a multi-body dynamics simulation (MBD) to determine yaw, roll and pitch response characteristics during a severe crosswind event. This one-way coupling approach mimics physical test conditions outlined in open loop test procedure ISO 12021:2010 that forms part of the vehicle sign-off criterion at Ford Motor Company. The methodology uses an overset mesh CFD method to drive the vehicle through a prescribed crosswind event, providing unfiltered predictions of vehicle force and moment responses that are used as applied forces in the MBD model. The method does not account for changes in vehicle attitude due to applied aerodynamic forces and moments. Traditionally, a vehicle’s crosswind response is simulated using curve-fits from quasi-steady-state aerodynamic tests across the yaw polar as input conditions for the MBD simulation. Comparisons are made between the one-way coupled and quasi-steady methodologies and physical test data obtained for two ‘all new’ vehicles developed at Ford Motor Company of Australia, the Ford Escort mid-sized Sedan and the Ford Everest large SUV, along with the Ford B-Max developed at Ford of Europe. Good agreement is demonstrated between the one-way coupled analytical and physical data for the vehicle response during the crosswind event. Whilst the quasi-steady approach tends to under-predict crosswind responses for all three vehicles, the one-way coupling approach yields predictions for yaw rate, roll rate and lateral accelerations that fall within the variability of experimental data. It is inferred that improvements in the predictive capability using the one-way coupling approach is related to the ability to model the transient aerodynamic response of the vehicle, as it enters and exits the crosswind event.