Flow and aero-optics around a turret. Part 2. Surface pressure based proportional closed loop flow control

As focused light passes through turbulent flow the light is distorted and the intensity is reduced. An extended study using active flow control to affect the turbulent region over the a flat aperture of a 3-D hemispheric turret was conducted in the Air Force Research Laboratory's Subsonic Aerodynamic Research Laboratory (SARL) wind tunnel at Wright-Patterson Air Force Base. The SARL experiments were performed at a Mach number of :3, which gives Reynolds number on the order of 2; 000; 000. At these Reynolds numbers the flow becomes highly complex and more challenging to study. A large database from previous work containing no control and open loop control cases provided a rich ensemble for plant model development based on low dimensional techniques such as the split-POD method of Camphouse (2007). PIV velocity data was acquired along with simultaneously sampled surface pressure data at various planes across the turret with and without control. Control authority was acquire by actuators mounted upstream of the aperture that generated a momentum flux in the flow around the turret. Simple proportional closed-loop control was performed using the bandpass filtered temporal POD mode coefficients of the surface pressure as the feedback signal. This paper shows that the active control reduced the root mean squared of the pressure fluctuations, shrunk the integral scales, and drove the flow towards homogeneity.