The separation of boundary layers in engine inlets and ducts, such as in ‘S’ ducts, can significantly compromise the performance of aircraft propulsion systems. For example, in engine inlets, the separation of the incoming boundary layer can result in reduced pressure recovery and unsteady loading on the engine fan blades. This can lead to fatigue and failure of components and may also result in aerodynamic stall on the compressor blades (Wygnanski 1996). The study presented herein focuses primarily on observations of the flow over an adverse pressure gradient where supersonic microjets are used to control flow separation. The geometry used for this study is a simple, diverging ‘Stratford’ ramp equipped with arrays of 400μm supersonic microjets. By activating these microjets, we were able to eliminate the separated flow with minimal mass flux less than 1.5% of the flow rate based on the boundary layer thickness.

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