Dielectric Barrier Discharge Plasma Actuator Thrust Measurement Methodology Incorporating Antithrust Hypothesis

Abstract

The thrust of the dielectric barrier discharge plasma actuator is the plasma body force minus the wall shear force, and it equals the net induced momentum. Thrust measurement simplicity makes it a good metric of the aerodynamic performance for active flow control applications. Uncertainty and non-repeatability issues with conventional test setups motivated development of a novel suspended actuator test setup and a measurement methodology consisting of a burn-in procedure followed by frequency scans at constant voltages. This approach led to observation of negative values of thrust, or “antithrust,” at low frequencies between 4 Hz and up to 64 Hz. The antithrust is proportional to the mean-squared voltage and is frequency independent. Departures from the parabolic antithrust curve are correlated with appearance of visible plasma discharges. The antithrust hypothesis is proposed. It states that the measured thrust is the sum of plasma thrust and antithrust. The magnitude of the antithrust depends on the actuator geometry, the materials, and the test installation. The dependence on test installation was validated by surrounding the actuator with a grounded large-diameter metal sleeve. A thrust data correction for antithrust enables meaningful comparisons between actuators at different installations. A strong dependence on humidity is also shown. The thrust significantly decreases with increasing humidity.