It is of interest to increase the efficiency of turbine and compressor blades for jet engines. There is much energy wasted by the flow around the tip of the blade, between the blade and the engine wall. Primary contributors to loss in this region are the tip leakage and passage vortices. We are interested in the effect that plasma actuators as an active flow control device has on these vortices, and how this effect compares with known passive flow control techniques, particularly partial suction side squealers.
A high speed linear cascade was designed and constructed to use one of the supersonic pumps in the main lab of Hessert Laboratory. This is a three blade cascade using PakB low pressure turbine blades. The center blade is cantilevered with a variable gap, 0 – 5% of chord. There are thirty pressure taps on the wall across the gap from the blade, and a five-hole pitot probe traverses a 100 point grid covering ½ the pitch and 1/3 of the span on the suction side of the blade approximately 1 chord downstream. The Reynolds number is varied between 100,000 and 500,000. Results of an uncontrolled blade, a blade with a partial suction side squealer, and a blade with a variety of plasma actuator configurations, actuated at a variety of unsteady frequencies are compared.
The plasma actuator is two electrodes that are separated by a dielectric material. One electrode is exposed to air, while the second is completely covered by the dialectric. When a high voltage a.c. amplitude is supplied to the electrodes the air ionizes in the region of largest electric potential, generally located at the edge of the exposed electrode. The presence of an electric field gradient causes the ionized air to produce a body force on the ambient air. Our actuator is shaped like the partial suction side squealer. It is milled out of copper clad circuit board.
Endwall Pressure contours are measured for a gap of 4% for Reynolds numbers of 100,000 and 500,000 for the baseline (no control case) and the passive flow control using a partial suction side squealer. Coefficient of pressure contours are also measured in the wake behind the blade.