Experimental closed-loop control of a detached boundary layer at high Reynolds number

A large variety of flow control strategies has been used in the last decades to avoid separation of boundary layers for, as major concern, aerodynamic benefits. The paper addresses closed-loop control of a quasi two-dimensional turbulent boundary layer with massive separation. The experiments are conducted in the LML boundary layer wind tunnel in Lille. Special attention is paid to the transient dynamics between the separation and reattachment regimes. For the control itself, 22 round air jets distributed in the spanwise direction upstream of the separation line are used as actuators. The jets generate co-rotating vortices which re-energise the near-wall region, and force the flow to reattach more or less depending on the actuation parameters.