Force Measurements on Plasma Actuators Using Phase-locked Particle Image Velocimetry

Abstract : Phase-locked Particle Image Velocimetry (PIV) has been used to investigate the time-dependent behaviour of a Dielectric Barrier Discharge (DBD) plasma actuator, excited by a sine-wave signal with peak-to-peak amplitudes between 7.2 kV and 10 kV, and frequencies of 2.5 kHz and4 kHz. Measurements were initially carried out in a 31.5 mm x 15 mm domain, resulting in a spatial resolution of 0.1072 mm, in 12 phase intervals throughout the excitation cycle. In order to improve the spatial and temporal resolution, additional measurements were carried out for a subset of the excitation parameters in an 8.1 mm x 6.1 mm domain, resulting in a spatial resolution of 0.0276 mm in 24 phase intervals. Momentum balance in a control volume surrounding the actuator has been used to estimate the body force based on the results of the PIV measurements. The results indicate that the maximum induced velocity and body force occur during the negative half-cycle of the excitation signal, with a phase lag relative to the excitation signal that grows when excitation voltage or frequency is increased. A smaller, secondary peak is observed in the induced body force, occurring during the positive half-cycle of the excitation signal. The results suggest that this peak is due to formation of a secondary high-velocity region due to local discharges near the grounded electrode. Two methods have been used to determine the shear force, resulting up to 25% variability in the estimated body force. Considering this variability, direct force measurements have been carried out using a precise balance to validate the results of the PIV-based control volume approach. The difference observed in certain conditions between the estimated body forces and those measured directly highlight the need for further improving the methodology for body force prediction based on PIV measurements.