Effect of Jet Pitch Angle of Vortex Generator Jets on Suppressing Flow Separation.

The vortex generator jet method as an active control technique of flow separation provides a time-varying control action to optimize performance under a wide range of flow conditions. The interaction between the jets and the freestream generates longitudinal vortices. The jets in this study were skewed at 90 deg to the freestream. The effect of jet pitch angle on suppressing flow separation was studied experimentally in three cases with the pitch angle set at 30, 45, and 60 deg. For the 60-deg case, longitudinal vortices move more rapidly apart from the lower wall than the other cases and therefore the 60-deg case is inferior to the others in the control of boundary layer separation. A pitch angle of 30 or 45 deg makes separation control more effective. In particular, for a pitch angle of 45 deg, the effect on suppressing flow separation persists further downstream.