Experiments with Vortex Generators applied to a Notchback Car Model

Abstract

An experimental study on a realistic 1:4 scale car model with a notchback is conducted. Vortex generators are attached to the roof at variable positions in order to analyze their effect on the aerodynamic drag. The experiments are conducted at a Reynolds number of three million. The effects of the vortex generators are evaluated by comparing the aerodynamic forces and the surface pressures. Furthermore, the flow field is investigated using stereo particle image velocimetry. In general the vortex generators increase the pressure level on the back light and trunk of the car. This results from the suppression of a recirculation bubble. The pressure increase depends on the position of the the vortex generators as well as their geometrical characteristics. The maximal achieved pressure coefficient with vortex generators is approximately CP = +0.15, which corresponds to an increment of ∆CP,max = +0.2. The increased pressure leads to a growth in the downward force of around 33%. However, the base pressure, which is mainly responsible for the aerodynamic drag, is only marginally affected about ∆CP ≈ −1%. Consequently, the force measurements show an increase in drag of about 1-4%. The PIV measurements show further, that the VGs suppress the recirculation bubble at the rear window and the upper trunk. Furthermore, the center of the spanwise counter-rotating vortices in the near wake behind the car are shifted further downstream and the off-surface stagnation point is stable but shifted upwards.