Control of the Turbulent Shear Layer Downstream of a Backward Facing Step using Nanosecond Pulse Driven Surface Plasma Discharges: Effects of Pulse Energy

摘要

The influence of pulse energy on nanosecond pulse driven dielectric barrier discharge (ns-DBD) plasma actuation applied to the 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 based on initial momentum thickness. 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 the most favorable as seen from momentum thickness growth and TKE distribution. Further analysis through the use of schlieren imaging suggests that depreciating control authority for the highest pulse amplitude of 0.88mJ/cm may be a result of either increased plasma three dimensionality resulting in non-uniform heating, or a thermal saturation mechanism (overheating). Additional theoretical studies are required to substantiate these claims and to decipher between the two.