Closed-loop Control of Vortex Shedding in a Separated Diffuser Using an Inverse Method

We propose a closed-loop control algorithm for vortex shedding in a separated diffuser. We introduce pulses of zero-net-mass injection (consecutive blowing and suction) together with an inverse vortex imaging method. This method estimates the circulation of a vortex in the separated region based on pressure at a limited number of observer points at the wall. The closed-loop algorithm determines when to start the pulse so that the vortex is pinched off with a size which minimizes the stagnation pressure loss. We examine the proposed method in a simplified flow by performing direct numerical simulations of two-dimensional diffusers. In order to investigate the robustness of the closed-loop control algorithm, we impose high frequency acoustic disturbance upstream of the separation point. The disturbances significantly reduce the effectiveness of open-loop control compared to the case where no external disturbances are added. By using closed-loop control, however, performance is once again substantially recovered in the presence of disturbances.