Navier-Stokes calculations of inboard stall delay due to rotation

Abstract

Momentum blade element methods, which have historically been used to predict rotor blade thrust, underpredict the power that is required for highly twisted rotors at high thrust levels. During a test of the V-22 tilt rotor blade conducted at the NASA Ames Research Center Outdoor Aerodynamic Research Facility (OARF), measurements of the thrust as a function of collective angle showed that the thrust levels achieved were higher than anticipated and drag levels at the high thrust levels were much lower than predicted. Because the maximum thrusting capability of the rotor in hover usually determines the maximum pay load of the vehicle, it is important to be able to accurately predict high thrust performance characteristics. A three-dimensional Navier-Stokes method was used to investigate the flow phenomenon that causes the increase in lift coefficients and reduction in drag coefficients obtained near the stall of a rotating blade. Comparison of the computational results with the experimental data indicates that this method can be used to predict thrust levels. The Navier-Stokes results indicate that flow separation near the hub is curtailed for a rotating blade compared with the momentum blade element predictions.