Inverse Technique for Vortex Imaging and Its Application to Feedback Flow Control

A simple vortex imaging algorithm using a least square method is proposed for feedback flow control. The position and the circulation of a vortex convected in a channel are identified from the time history of pressure at a limited number of points on the wall. The capabilities of the algorithm are demonstrated using two-dimensional direct numerical simulations. A few observer points on one side of the wall are sufficient to detect the position and the circulation of a compact vortex to a reasonable degree of accuracy. This inverse algorithm is introduced to feedback separation control for a diffuser flow. The algorithm is modified for a curved channel, and the so-called "estimator-corrector" and "fast algorithm" are applied to reduce the uncertainty of prediction with less computational time. The DNS results demonstrate that the feedback control using the inverse technique can enhance the robustness against unsteady disturbances and lessen stagnation pressure loss.