The countercurrent mixing layer: Strategies for shear-layer control

The dynamics of a spatially developing countercurrent mixing layer is studied in a parameter space including velocity ratio, density ratio, and convective Mach number. Under an appropriate set of operating conditions, the countercurrent mixing layer displays strong global oscillations which significantly alter the spatial development of the flow. Evidence is presented which suggests these oscillations are associated with a transition from convective to absolute instability. Countercurrent mixing is examined as a novel control strategy of supersonic free shear flows. Experiments indicate that counterflow can be used effectively to enhance mixing in supersonic axisymmetric jets. It is also demonstrated that counterflow can be successfully employed for the thrust vector control of high-speed rectangular jets.