Realistic turbulent flow conditions, typical for highway driving, can have a significant effect on vehicle aerodynamic performance. This is an important topic for the vehicle aerodynamics community, and is attracting increasing attention. On-road wind velocity measurements show that in the presence of ambient wind or upstream vehicles, turbulence is seen with amplitudes often up to 10 % of the vehicle driving speed, measured using the standard deviation of velocity component fluctuations. The turbulent flow structures have a dominant length scale near the size of the vehicle, e.g., 1 to 10 m, measured using the integral turbulence length scale. These turbulent flow structures cause a significantly non-uniform flow environment for the vehicle and disrupt many of the most important flow features around the vehicle, such as wakes, attached vortices, under body separations and impingements, and backlight separation. These features are intentionally affected by design changes made by aerodynamicists during the vehicle development process in order to optimize aerodynamic efficiency and handling. In this paper, a Jaguar XJ saloon is tested using transient aerodynamics simulations with realistic onset flow conditions. The yaw angle is maintained at zero degrees to isolate the effect of disruption due to upstream turbulent conditions from the effect of mean crosswind. The impact of upstream turbulence on the aerodynamic performance is evaluated, and analysis of the key separated flow structures on the vehicle shows the regions of influence of the realistic turbulent conditions.
Effect of non-uniform flow conditions on vehicle aerodynamic performance
2013
16 Seiten, Bilder, Tabellen, 25 Quellen
Aufsatz (Konferenz)
Englisch