An experimental study on base pressure behavior during bistability characterisation for a bluff body vehicle close to the ground

Abstract

The present experimental investigation is concerned with the existence of Bi-stability behaviour at various ground clearances in the wake of Square Back Ahmed Body geometry (SBAB). The experiments were performed at a Reynolds number of 7.2 × 104 in a subsonic open-type wind tunnel facility. The raw readings from the pressure scanner alone were used to predict the existence of bistability character. The bistability behavior in the wake was explored in two different ways (i) The conventional base-pressure contours and pressure gradient plot, and (ii) The wavelet analysis. The minimum ground clearance for the wake to exhibit bistability was found to be 0.468H, much higher than the values determined in the previous experimental works. The discrepancy was due to relatively high turbulence intensity in the test section and experimental setup. We also found that the bi-stability switching rate was found to increase with a decrease in ground clearance. The wavelet analysis helped in determining the existence of long time-scale frequencies associated with the Bi-stability behavior.