Effects of pulse energy on shear layer control using surface plasma discharges

The influence of pulse energy on nanosecond pulse driven dielectric barrier discharge (ns-DBD) plasma actuation applied to a turbulent shear layer downstream of a backward facing step (BFS) is examined experimentally. The ns-DBD control mechanism, which is believed to be primarily thermal in contrast to most other flow control actuators, has been demonstrated in various high speed shear flows yet questions on fundamental physics and scaling remain unanswered. In this work, ns-DBD pulse amplitude is varied between 0.13mJ/cm - 0.88mJ/cm per pulse in order to understand its effects on the excitation of a turbulent shear layer. This work is carried out at a fixed actuation frequency of 1000Hz which corresponds to St_θ=0.005. Both mean and phase-averaged data indicate a preference for the 0.33mJ/cm and 0.56mJ/cm pulse amplitudes. However, further analysis concludes that 0.33mJ/cm is most favorable as seen from momentum thickness growth and TKE distribution. It is unclear whether depreciating control authority for the highest pulse amplitude of 0.88mJ/cm is the result of increased plasma 3-dimensionality or some other thermal saturation mechanism.