Separation-Control Mechanisms of Steady and Pulsed Vortex-Generator Jets

Vortex-generator jets have been used to remove an open separation on the suction surface of blades within a linear compressor cascade at high incidence. Steady jets removed the separation with a jet velocity ratio of 70%, reducing the loss coefficient by 60% relative to the uncontrolled case. Pulsed jets tested over a range of reduced actuation frequencies also yielded a reduction in the loss coefficient. The mechanisms by which steady and pulsed vortex-generator jets delay separation and reduce loss were explored using particle-image velocimetry measurements. The results suggest that the mechanisms by which steady and pulsed vortex-generator jets achieve separation control are different. With steady blowing, streamwise vortices mix the separated boundary layer. In the pulsed case, however, at least some control authority is a result of spanwise structures, the roll up of which is encouraged by actuation at appropriate forcing frequencies.