PIV measurements of the effect of pitch and skew on a circular orifice synthetic jet in a turbulent boundary layer

PIV results are presented for synthetic jets with different orientation with respect to the outer flow. For all the cases, for an outer flow velocity of 28ms-1, the velocity ratio between the freestream and the exit peak velocity of the jet was set to 1.2, the Strouhal number to 0.069 and the boundary layer thickness was measured to be 9 times the diameter of the orifice. Differences in the roll-up process and in the evolution of the structures formed in the interaction with the boundary layer are presented at a location 10D downstream of the orifice for normal, pitched and pitched and skewed jets. For the normal and pitched synthetic jet it is shown that vorticity in upstream edge of the ejected structure is suppressed and that truncated hairpin like structures are produced consistent with the flow structures typically observed in flow visualization studies. For the pitched and skewed jet, the resulting hairpin structure is asymmetric about the streamwise vertical plane, with significantly greater vorticity in the upper leg of the hairpin. This type of structure is similar to that produced by conventional vane vortex generators or steady air jet vortex generators and shows promise as an optimal flow control configuration.