Propeller Performance at Large Angle of Attack Applicable to Compound Helicopters

Abstract

An experimental dataset is presented of propeller performance in static condition and at low subsonic airspeeds for various angles of attack up to 90 deg. Numerical investigation through a Reynolds-averaged Navier–Stokes computational fluid dynamics model revealed the mechanisms behind performance changes with advance ratio, angle of attack, and configuration changes. The experimental dataset was found to be free of major errors and is very suitable for validation of propeller models. Furthermore, aerodynamic interaction with an upstream wing was tested with the propeller and wing normal to the flow, to represent the interaction occurring with a time-averaged main rotor slipstream on a compound helicopter. From numerical investigation it was concluded that the results are qualitatively representative of this interaction. The experimental data showed that addition of the wing results in a net reduction of all propeller performance quantities, with thrust reducing up to 20%. Thrust decreasing and thrust increasing mechanisms were found numerically. For most tested operating conditions, the wing resulted in a small decrease of propeller thrust-over-power ratio. Decreasing propeller advance ratio, increasing wing distance, and increasing flap deflection generally decreased the effect of the wing on thrust and power; however, the influence of flap deflection was found to be small.