Drag reduction on a simplified 3D bluff body

A complete flow control over road vehicles is difficult to achieve because of different phenomena occurring in flow evolution, i.e. the wheel rotation and ground effect deeply influence the flow features. In spite of this, the problem can be approached following different strategies considering both passive and active flow control techniques. The flow around bluff body road vehicle exhibits a massive separation region and as a consequence the drag is mainly due to pressure losses. The total aerodynamic drag of such bodies can be roughly split into three main contributions. The rolling tire account for up to 25-30% whereas the rear part gives rise to 40-45% of the total drag. The remaining is due to the underbody flow and interferences. The wake structure is greatly influenced by the rear geometry of the body that determines the pressure field in this region. As showed by Ahmed [1] and by Iuso [2] the afterbody geometry plays a key role for the drag contributions and also for drag reduction when passive solutions are adopted. In cases where a square back rear part is imposed by different requirement such as internal space in commercial vehicles, passive or active control techniques can be used to achieve drag reduction. Passive and active vortex generators as those used by Aider et al [3] and piezoelectric vortex generators as proposed by Orazi et al. [4] can be adopted. Also synthetic jets located in the body rear part as done by Park et al. [5] or continuous blowing slots as done by Rouméas et al. [6] have been also used. Since a favorable energy budget is an essential requirement for a real application of active flow control the technique efficiency is of crucial importance. From this point of view very low energy absorption devices or direct drag alleviation are promising possible solutions. In the present study a simplified car geometry has been chosen as a reference shape and a wake control system has been designed based on continuous or synthetic jets. The results of preliminary CFD analysis focused on the investigation of natural and controlled flow behavior are presented here. Moreover, this study has allowed the design of the physical experiment in the wind tunnel.