Control of three-dimensional wakes behind simplified models of blunt-based vehicles

Abstract

Two general types of behaviors have been identified in terms of the drag coefficient, as the value of Cm increases. For weak blowing rates, a mass injection mechanism acts filling the recirculation bubble and increasing its length, leading to the subsequent decrease of the drag force. Eventually, at higher blowing rates, such effect is reversed and the recirculation region size reduces, leading to an increase of drag. The latter behavior, which will be denoted as momentum regime, produces important changes on steady RSB modes, translating the wake deflected position from horizontal to vertical directions for some blowing configurations. The effect of the blowing density on the aforementioned mechanisms will be also discussed, showing that a light gas reduces more efficiently the drag coefficient than heavier gases. Besides, a second passive strategy is presented, whereby curved rear cavities, designed by means of topological optimization processes, are tested on the Ahmed body for different yaw angles, showing a larger drag reduction and bi-stable dynamics mitigation than classical solutions consisting of straight cavities or flaps. [1] H. Choi, et al. Annual Review of Fluid Mechanics 46:44-68, 2014. [2] S. R. Ahmed et al. SAE Tech. Rep. No. 840300, 1984. [3] M. Grandemange et al. Journal of Fluid Mechanics, 722:51-84, 2013.