Vane Separation Control in a Linear Cascade with Area Expansion using AC DBD Plasma Actuators

The purpose of this dissertation is to investigate loss generation in a linear cascade with cross-sectional area expansion. The cascade inlet Mach number ranged from 0.4 to 0.6, and the vane chord Reynolds number ranged from 0.9 to 1.5 million. Three cascade designs with varying amounts of area expansion, providing different degrees of adverse pressure gradient, are examined. The initial surface flow visualization experiments and optical flow analysis revealed a hub separation region on the suction side of the vanes. Previously published research and preliminary CFD simulations agree with these initial flow findings. Passive and active forms of flow control are employed to mitigate losses in the system. Plasma actuators are placed on the suction sides of the vanes, just upstream from the flow separation location as an active form of separation control. A 5-hole pitot probe is used for quantitative data measurements. The effects of plasma actuation on the pressure loss coefficient and flow turning angle is measured. The result is that the plasma actuator’s separation control increases the dynamic pressure in the passage between the vanes, resulted in a more spanwise-uniform flow turning angle, and effectively lowering the loss coefficient compared to the baseline. A passive approach to loss mitigation through the use of fences is employed to mitigate secondary flows from contributing to the generation of vortices in the hub-corner region. Plasma actuators are utilized to further improve flow quality and separation for the fenced cases. The addition of the fence to the vane suction surface creates a blockage increasing losses in its wake. Surface flow visualization, optical flow analysis, and wake pressure measurements are taken for the concurrent fence and plasma actuation case. The result of this study is that the fence successfully mitigates the secondary flow from the hub and produces a 2-D separation location on the vane suction surface. The plasma DBD actuation successfully reattaches this 2-D separated flow. However the concurrent use of the fence and plasma DBD actuation adds to the overall losses in the system. Thus, the unfenced vane under the effects of plasma actuation separation control most effectively decreases losses through the cascade.