Predictive Modelling of Engine Inlet Distortion in Crosswind Conditions

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The intake of aircraft engines is constructed to provide a steady and uniform flow over a wide range ofoperating conditions. Nacelles are designed to optimize cruise efficiency while meeting the stringentoperational requirements at off-design conditions. One of the most critical operating points occurs on theground with severe crosswinds when the aircraft is at rest. In this setup, the crosswind causes a stagnation pointto occur on the outer nacelle, the flow then accelerates and transitions around the lip before entering the engineat a near-sonic speed. The negative pressure gradient at the engine inlet results in flow separation, whichdistorts the incoming flow stream; at sufficiently large distortion levels, stall or aerodynamic instabilities of thefan blades may arise. The accurate prediction of the engine inflow distortion is extremely difficult as it involveslaminar-to-turbulent transition, complex geometry and pressure gradients and flow separation. This projectseeks to improve on existing transitional models to accurately determine the onset of transition on a complexthree-dimensional nacelle, and thus improve the prediction accuracy of inflow distortion at these criticaloff-design conditions.