Boundary feedback flow control: Proportional control with potential application to aero-optics

A large percentage of the losses in performance and effectiveness of airborne optical systems are caused by turbulence. In an effort to reduce these adverse effects in airborne optical systems, we are exploring the use of both open-and closed-loop flow control over a cylindrical turret. A series of experiments were performed at a Reynolds number of 2̃106, based on the turret's diameter and freestream velocity, which corresponds to a Mach number of 0.3. The three-dimensional turret contained an actuation system that consists of 17 synthetic jets placed upstream from the leading edge of the aperture. Initially, a large database containing no control and open-loop control was obtained. These data sets provide a rich ensemble for the development and application of a simple proportional closed-loop control with the use of proper orthogonal decomposition. Surface pressure measurements were acquired across the aperture region for all cases studied. Results from the open-loop test demonstrate a reduction of 19.6% in the root-mean-square values when compared to the baseline case. The closed-loop flow control results show that the root-mean-square pressure fluctuations are reduced by 25.7%, the integral scales are significantly reduced, and the flow is driven toward homogeneity.