Plasma Actuator Force Measurements

Abstract

In previous work at the U.S. Air Force Academy, the phenomenology and behavior of the aerodynamic plasma actuator, a dielectric barrier discharge plasma, was investigated. To provide insight into the phenomenology associated with the transfer of momentum to air by a plasma actuator, the velocity distributions upstream and downstream of a plasma actuator with an induced boundary layer were measured using freestream velocities of approximately 4.6 and 6.8 m/s for a range of frequencies (5-20 kHz) and voltages (5-10-kV amplitude). The body forces on the air were calculated using a control volume momentum balance. In a second experiment, time-averaged results were also obtained by measuring the reaction force using a pendulum. A third experiment uses an accelerometer to gain insight into the time-dependent forces or, more specifically, the direction of the forces. The results show that the body force acts within the first 4 mm above the surface of the actuator (within the boundary layer). For a constant peak-to-peak voltage, the body force is proportional to frequency, producing a constant impulse per cycle, and the energy dissipation per cycle and efficiency are independent of frequency. The time-dependent measurements support the theory that the body force of the actuator consists of one large push followed by one small pull during each cycle.