The development of synthetic jets for enhanced control of separated flows

This paper details the findings of an experiment that has attempted to alter the unsteadiness levels in the post-burst region on a 60° angle of sweep, delta wing configuration. The experiment made use of an array of synthetic jet actuators embedded in the wing leading edge to try and inject coherent structures into the shear layer that separates from the leading edge before rolling up to form the vortex which subsequently bursts at a location downstream of the wing apex. The frequencies used to actuate the flow were related to, and an order of magnitude bigger than the dominant frequencies found in the unsteady region that was to be altered. An array of 137 pressure tappings on a semi-span of the wing was calibrated and used to acquire unsteady pressure data. The results are presented in terms of both the distribution of rms pressure over the wing surface and in terms of the spectral energy of the flow at discrete points on the wing (PSD vs. frequency plots). It is shown that oscillatory actuation of the shear layer before it separates can be an effective technique in reducing the unsteadiness typically found in post-burst regions on highly swept wings. The results indicate that both frequency of actuation and jet to free-stream velocity ratio play a major part in how effective the technique can be in reducing rms pressure levels. It is shown that for velocity ratios of less than 1, it is possible to decrease the peak PSD value at a point on the wing by up to 60% and in turn produce a 30% decrease in rms pressure over a large percentage of the wing area that is in the post-burst region.