Effect of Vortex Generator Jets with T-Shaped Orifices on Separation Control

Abstract

Jets issuing through small holes in a wall into a freestream have proven effective in the control of boundary layer separation. Longitudinal vortices are produced by the interaction between the jets and the freestream, and this technique is known as the vortex generator jet (VGJs) method. In the case of VGJs with circular orifices, the jets are pitched at an angle of 45 deg or less to the wall for the effective suppression. However, a small jet pitch angle causes the complex operations in manufacture process of the jet orifice installed in the practical devices. In this study, the VGJs with T-shaped jet orifices were practically applied to flow separation control of a two-dimensional diffuser, and the suppression effect for the T-shaped orifice was compared to that for the circular orifice in the case of a large jet pitch angle (60 deg). The T-shaped orifices produce the counter-rotating vortex pair which has the different strength between positive and negative vortices, and the longitudinal vortices exist near the lower wall. Therefore, the VGJs with T-shaped orifices provide more effective momentum transfer to the boundary layer and make the separation control effective, in contrast to the VGJs with circular orifices.