Generating Mechanism of Longitudinal Vortices Using Pulsed Vortex Generator Jets

Jets issuing through small holes in a wall into a freestream have proven effective in the control of boundary layer separation. Longitudinal (streamwise) vortices are produced by the interaction between the jets and the freestream. This technique is known as the vortex generator jet method of separation or stall control because it controls separation in the same general way as the well-known method using solid vortex generators. For the vortex generator jets, the shape and the downstream development of longitudinal vortices are varied by issuing jets discretely (pulsed jets). In order to understand the reasons why the vortices for the pulsed jet case behave in a manner different from those for the steady jet case, velocity measurements were carried out in various phases of pulsed jets. The longitudinal vortices produced by pulsed jets have a stronger influence of jet pitch angle in comparison with the steady jet case. Pulsed jets promote the interaction between adjacent vortices and therefore the shape and the downstream development of longitudinal vortices are different from those of the steady jet case.