Boundary Layer Separation Control With Fluidic Oscillators

Fluidic oscillating valves have been used in order to apply unsteady boundary layer injection to repair the separated flow of a model diffuser, where the hump pressure gradient represents that of the suction surface of a highly loaded stator vane. The fluidic actuators employed in this study consist of a fluidic oscillator that has no moving parts or temperature limitations and therefore is more attractive for implementation on production turbomachinery. The fluidic oscillators developed in this study generate an unsteady velocity with amplitudes up to 60% RMS of the average operating at non-dimensional blowing frequencies (F+) in the range 0.6 < F+ < 6. These actuators are able to fully reattach the flow and achieve maximum pressure recovery with a 60% reduction of injection momentum required and a 30% reduction in blowing power compared to optimal steady blowing. PIV velocity and vorticity measurements have been performed that show no large-scale unsteadiness in the controlled boundary layer flow.