Rotating Stall Control in an Axial Fan with Pulsed-Direct-Current Plasma Actuation

Abstract

The use of dielectric barrier discharge plasma actuators to suppress traveling stall cells and thereby improve stall margin is examined. This involved the design and construction of a nonconductive high-solidity fan facility. The experiments were meant to support the application of similar systems in transonic axial compressors. Eight 63.5-mm-long plasma actuator segments were installed in the casing over the blade row at three axial locations that were indicated in the literature to be optimum for stall margin improvement. Independent control of fan revolutions per minute (RPM) and mass flow was used to set conditions that produced traveling stall cells. These were documented using an azimuthal array of microphones. The microphone pressure time series were spatially correlated to reveal the coherent wave packets. Different azimuthal combinations of the plasma actuators were investigated from a single actuator to all eight. A single actuator reduced the local spatial correlation metric (SCM), a measure of stall cell activity, by 40% and the azimuthally averaged SCM by 30%. A “memory effect” on the stall cell suppression was revealed, and it persisted for approximately 180° of the casing azimuth. The effect of the plasma actuator axial location was investigated at the design RPM and at two off-design RPMs. At the design RPM, the two most optimum locations were slightly upstream of the blade row and at the midchord of the blade row. This changed for the off-design conditions. For the range of the fan RPMs and actuator locations investigated, the stall margin improvements ranged from 1.63 to 5.45%. Finally, a plasma actuator stall extension model is presented for relating the required plasma actuator body force to the achieved stall margin improvement.