On the ground effect in passive control using deflectors at the rear part of an Ahmed body

Drag measurements were performed over an Ahmed body with a 25-degree slant angle modified with rigid deflectors at the top rear edge. Experiments were conducted on both a wind tunnel and a towing water tank in the range of Reynolds numbers based on the height R e H = 30 × 1 0 3 − 170 × 1 0 3 . In the wind tunnel experiments, drag measurements were acquired at two ground clearances: a nominal height, and a larger distance 14 times the nominal one to minimize the ground effect. The inclusion of a deflector with an inclination in the range of α = [ − 8 ° , − 4 ° ] decreases the drag coefficient by up to 27% over the base case without deflector. Furthermore, an analytical correlation was developed to predict the drag coefficient as a function of Reynolds and deflector angle for each ground clearance. Additional 2D-PIV measurements obtained in the towing tank confirmed that the circulation of the C-vortex is significantly reduced compared to the base case. These results demonstrate that the observed drag reduction is primarily associated with a weakening of the induced wake structures.