Control of the flow in a trapped vortex cell

A trapped vortex cell, (TVC), is a flow control device consisting in a cavity embedded on the upper surface of an airfoil, designed to trap a steady vortex. By the interaction with the vortical cell's ow, the incoming boundary layer becomes more energetic, and it is thus less prone to separation. Wind tunnel tests by De Gregorio et al. [2] and by Lasagna et al. [1] have shown that to make this control effective the cavity flow itself must be the target of a control action. In particular, the latter authors have shown that the airfoil drag can be substantially reduced with respect to the clean airfoil by applying suction into the cavity region and that this technique is superior to a classical boundary layer suction system, for the same suction flow rate. One goal of this work is to further investigate on the drag reduction mechanism of the TVC with suction technique. Furthermore, a second control technique, based on a synthetic jet device (SJ) which injects momentum into the cavity in order to energize the vortical cell's flow, is considered. Interest in this technique is raised since it is far more effcient than steady suction.