The attenuation of cavity tones using plasma actuators

Description/Abstract

The aeroacoustic environment of an open cavity with length-depth (L/D) ratios of 0.5 and 1.0 was studied
with and without plasma actuators. The study was conducted through low speed wind tunnel experiments at
freestream velocities between 10m/s and 20m/s corresponding to Reynolds numbers, based on the depth of the
cavity, of 2.7×104 to 6.7×104. The oncoming boundary layer was turbulent with a thickness typically of 0.1D.
The fluid flow inside the cavities was studied using a range of measurement techniques. These include oil flow,
particle imaging velocimetry (PIV) and surface mounted microphone measurements. For acoustic control an
array of paraelectric plasma actuators were located on the approaching surface to the cavity, aligned with the
direction of the oncoming flow. Results show that the plasma actuators lead to a significant attenuation of the
dominant cavity mode. The PIV surveys around the electrode elements reveal vortical structures produced by
the plasma actuators. It is surmised that these structures are convected downstream with the mean flow and
produce disturbances similar to that of vortex generators. This affects the convection of discrete vortices in the
cavity shear layer, disrupting the mechanisms that allow the cavity to produce tones. Results also show that for
any given geometry and input voltage to the plasma actuator the attenuation in the dominant mode reduces
with increasing flow speed.