On the Use of Thermal Energy Deposition for Active Control of a Turbulent Mixing Layer

Nanosecond dielectric barrier discharge (ns-DBD) plasma actuators are known to control flows through thermal energy deposition. However, unlike momentum addition type actuators (e.g. ac-DBDs), the relationship between control authority and the amplitude of energy deposition in the flow is not well understood. This investigation quantifies the density/temperature gradients introduced as a function of actuation parameters using background oriented schlieren (BOS) in a low-speed turbulent mixing layer. The effect of changes to the mean properties of the flow are modelled by linear stability theory (LST) using a 2-D inviscid model of the mixing layer with variable mean temperature & density profiles that are obtained from BOS. At increased forcing amplitudes, a drop in the growth rate (-α_i) of the peak unstable mode is noted, as well as a shift in the neutral point to lower frequencies. These results suggest that excessive changes to mean temperature/density (due to high amplitude forcing) can have detrimental effects on control authority.This implies that there is some optimal level of energy deposition for controlling a given flow