Mixing enhancement due to global oscillations in jets with annular counterflow

A novel control technique is described which leads to the enhancement of mixing in axisymmetric jets. The approach relies on the self-excitability of the jet and does not require elaborate feedback control schemes or actuators. Self-excited global oscillations are established in the jet by applying suction to an annular cavity placed around the jet periphery. These oscillations are responsible for enhanced mixing between the jet and the surrounding fluid, and can be maintained at relatively low levels of counterflow. Furthermore, the global oscillations and increased mixing appear to be insensitive to the jet initial conditions. The present study included jet Reynolds numbers between 3.4×10 4 and 1.1×10 5 for initially laminar and turbulent separated shear layers