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. The vortex generator jet method is active control of flow separation that has the ability to provide a time-varying control action to optimize performance under wide range of flow conditions. In this study, the suppression effect of the jet orifice shape of vortex generator jets on flow separation in the diffuser is investigated for three types of jet orifice (circular, triangle and square orifices). The triangle orifice makes strong the vorticity of longitudinal vortices and effective the pressure recovery in the diffuser in comparison with the other orifice shapes. Furthermore, it is found that the orifice shape of vortex generator jets causes the different tendency of the pressure recovery in the downstream direction.

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