Tip Clearance Flow Control in a Linear Turbine Cascade Using Plasma Actuation

Abstract

This research examines the use of passive and active on-blade flow control to reduce the unwanted losses associated with the blade tip clearance flow in a stationary, rectilinear turbine cascade. A SDBD plasma actuator and a passive partial suction-side squealer were tested over a Reynolds number range from 5.3×10 4 to 1.03×10 5 at a fixed tip clearance of 2.18 percent of axial chord. The pla sma actuator was designed to mimic the beneficial effects of the suction-side squealer ti p, while removing the negative aspects of the passive squealer design, including blade degradation flow recircul ation or potential blade-wall contact. The flowfield was documented with five-hole-probe measurements at 1 axial chord downstream of the test blade and within the clearance using wall pressure taps located on the endwall opposite the blade tip. These tests allowed the loss associated with the flow and the change in this loss with a pplied flow control to be recorded. The plasma actuator caused an improvement in the downstream flow, with a reduction in the total pressure loss coefficient within the tip leakage vortex ranging between 2% to 12%, depending on Reynolds number, while the passive squealer showed a change of approximately 40%. On the endwall within the clearance, the plasma actuator generated a 19% peak increase in wall static pressure while the passive squealer caused a maximum increase of 52%. These results show that the plasma actuator was able to favorably mitigate the adverse effects of the tip clearance flow in a similar manner as the squealer tip, withou t the drawbacks of the passive squealer method. Although less effective than the squealer tip, the positive results of the plasma actuator show that this type of flow control is suitable as a means of reducing the tip clearan ce flow loss.