Control of Turbulent Flow Over an Articulating Turret for Reduction of Adverse Aero-Optic Effects

Turbulent flows such as wakes and shear layers are highly detrimental to the intensity of any collimated light beams that pass through these regions. The work presented in this thesis utilized suction flow control to help mitigate the adverse affects of the wake and shear layer over a flat aperture on the hemisphere of a three dimensional turret. The hemisphere of the turret was capable of dynamically articulating in two degrees of freedom: pitch and azimuthal rotation. The experiments were performed in the Syracuse University wind tunnel at a Mach number of 0.1, giving a Reynolds number of 500,000. Steady suction at various amounts were initially implemented for both static and dynamic pitching cases. Abatement of the wake above the aperture of the turret was seen for open loop suction actuation in both cases, demonstrating that for our conditions the suction system has enough control authority to reduce the turbulence levels. Building upon this success, a simple proportional closed loop controller was constructed to improve the efficiency of the actuation system by reducing the amount of suction required to achieve the same level of turbulence abatement as with the open loop control. The overall objective of the controller was to drive the velocity fluctuations over the aperture of the turret to zero. The next set of experiments fixed the pitch angle and dynamically rotated the hemisphere in the azimuthal direction. Like the pitch tests, steady suction actuation applied over the top of the turret was able to diminish the size of the wake. A multiple-input-multiple output closed loop controller was then employed with the objective of reducing the velocity fluctuations over the aperture of the turret. By dividing the actuation into two separate zones, the MIMO controller was able to more efficiently decrease the turbulent levels over the aperture when compared to the open loop case. Additional suction control tests were performed over a stationary turret in the Air Force Research Laboratory wind tunnel at Wright-Patterson Air Force Base. Direct measurements of the aero-optic effects were taken via a Malley probe at a fixed pitch angle with and without suction control at a Mach number 0.3, and a corresponding Reynolds number of 2,000,000. Reduction of the aero-optic effects in this test demonstrated that suction control is a practical control input to reduce the near field wavefront abberations due to the turbulent flow over the aperture