Design for vehicle handling requires prediction of the aerodynamic lift on the front and rear tires where they contact the road, as well as the side loads and pitch, roll, and yaw moments that determine vehicle stability. These forces and moments are needed at a range of static crosswind conditions or under dynamic crosswind inputs. Under all conditions, these forces and moments are highly transient for most vehicles due to the strong sensitivities of the underbody and rear wake flow behavior to small fluctuations in pressure or onset flow.
Matching the true road conditions for high-performance vehicles is a major limitation of physical testing using wind tunnels. Realistic effects of vehicle motion and onset flow conditions cannot be included in a wind tunnel test. In a wind tunnel test, expensive moving-ground emulation systems consisting of belts and suction/blowing systems are used to approximate the effect of the vehicle motion on the road, and the effect of onset flow conditions is approximated by testing at a range of static crosswind (yaw) angles. However, wind tunnels are not equipped to accurately measure the transient aerodynamic loads that affect driver perception of vibration, response, and stability. These approximations create major limitations on the aerodynamic development of vehicles for optimizing handling attributes. Vehicle handling must then be assessed very late in the design process using road testing of final-stage prototypes.
The need for accurate prediction of transient forces and moments under dynamic onset conditions is also very challenging for traditional simulation tools. However, PowerFLOW is inherently transient and naturally handles these conditions. Time-accurate pressure fluctuations in the sensitive underbody and rear wake regions are simulated accurately, leading to prediction of transient response. The accuracy of PowerFLOW for handling attributes has been proven through industry validation compared to moving-ground wind tunnel tests with static crosswind conditions. Simulations can include dynamic onset conditions and the effect of other vehicles — conditions that cannot be produced in wind tunnels.
