Plasma actuators for separation control of low-pressure turbine blades

This work involves the documentation and control of flow separation that occurs over turbine blades in the low-pressure-turbine (LPT) stage at the low Reynolds numbers typical of high-altitude cruise. We utilize a specially constructed linear cascade that is designed to study the flowfield over a generic LPT cascade consisting of Pratt and Whitney "Pak B" shaped blades. The center blade in the cascade is instrumented to measure the surface-pressure coefficient distribution. Optical access allows laser-Doppler-velocimetry measurements for boundary-layer profiles. Experimental conditions were chosen to give a range of chord Reynolds numbers from 104 to 105, and a range of freestream turbulence levels from u'/U-infinity = 0.08 to 2.85%. The surface-pressure measurements were used to define a region of separation and reattachment that depends on the freestream conditions. The location of separation was found to be relatively insensitive to the experimental conditions. However, the reattachment location was very sensitive to the turbulence level and Reynolds number. In the absence of separation, excellent agreement was found between the measured pressure distributions and predictions from Euler simulations. Separation control was performed using a single-dielectric-barrier-discharge plasma actuator that is placed at different chord locations, upstream of the separation line. The actuator is designed to produce a steady two-dimensional jet, which is locally parallel to the blade surface. This is intended to add momentum to the near-wall boundary layer. Reattachment occurred in all cases. The amplitude level of the actuator was varied to determine its effect on the reattachment location.