Consistent Drag Prediction with CFD for a Vehicle with Bimodal Wake Cycling

The vehicle wake region is of high importance when analyzing the aerodynamic performance of a vehicle. It is characterized by turbulent separated flow and large low-pressure regions that contribute significantly to drag. In some cases, the wake region can oscillate between different modes which can pose an engineering challenge during vehicle development. Vehicles that exhibit bimodal wake behavior need to have their drag values recorded over a sufficient time period to take into account the low frequency shift in drag signal, therefore, simulating such vehicle configurations in CFD could consume substantial CPU hours resulting in an expensive and inefficient vehicle design iterations process. As an alternative approach to running simulations for long periods of time, the impact of adding artificial turbulence to the inlet on wake behavior and its potential impact on reduced runtime for design process is investigated in this study. By adding turbulence to the upstream flow, the wake can be prevented from settling into a particular mode and will instead rapidly cycle between modes, which may not only allow the drag to converge to a steady average value in a much shorter simulation time but also prevents bimodal drag behavior from going undetected in the form of early simulation convergence and inconsistent variation across different vehicles. With a more reliable average drag value output from simulations, informed decisions on vehicle configuration can be made during the development phase.