Flow field induced by a dielectric barrier discharge plasma actuator analyzed with bi–orthogonal decomposition

Abstract

A typical dielectric barrier discharge (DBD) plasma actuator generates complex periodic flow structures in burst mode. Efficient use of these actuators depends on clear understanding of the relationship between the operational parameters of the actuator and flow structure. The present study reports the temporal and spatial evolution of these flow structures by utilizing the bi-orthogonal decomposition (BOD) technique. The flow induced by the actuator is captured using a time resolved particle image velocimetry (2D–2C–TR–PIV) system. The BOD of flow field is carried out using instantaneous velocity field data. The DBD plasma actuator is operated at different combinations of duty cycle, α (50% ≤ α ≤ 90%), and burst frequency, fb (10 Hz ≤ fb ≤ 90 Hz). The modal energy content is used to characterize the flow field as a function of operating variables, i.e., α and fb of the actuation signal. The mean mode of the decomposition successfully approximates the time averaged behavior of the induced flow field. The mean mode energy level increases with the increase in both α and fb with a more pronounced effect observed as a function of fb. The coherent structures are located close to the near wall at high burst frequency. The non-dimensional entropy decreases with the increase in both α and fb with a more pronounced effect of fb than that of α. The decrease in entropy value indicates that space–time complexities are reduced at higher burst frequency. The topos of higher order modes reveal the presence of coherent structures that grow in time and convect along the wall like a train of vortices. The chronos of mode 2 and mode 3 is locked in with respect to the burst frequency. However, the chronos of mode 4 and mode 5 shows frequency doubling at lower burst frequency actuation and frequency halving at higher burst frequency actuation. The entropy value or space–time complexity of flow structures generated by DBD plasma actuator is related to the nonlinear vortex interaction mechanism, i.e., period doubling and period halving of chronos.