A Contour Coupling Methodology for Helicopter Hover Performance Analysis

This paper introduces a novel contour coupling methodology within a hybrid free vortex wake and Computational Fluid Dynamics solution procedure for helicopter rotor blades in hover. Coupling between the outer vorticity-embedded potential flow solution and the inner Reynolds-Averaged Navier-Stokes solver is achieved through the radial distribution of circulation along the rotor blade. The most common approach to obtain the blade circulation distribution is to apply the classical Kutta-Joukowski lift theorem with the blade lift obtained from surface pressure integration. In the present approach, the circulation is determined by integrating around closed sectional contour paths of particular geometry. This is a generalized form of the Kutta-Joukowski theorem, however without the associated flow assumptions. The accuracy of both the new and traditional coupling approaches is demonstrated by comparison against model rotor performance data for the UH-60A blade and the tapered-tip variant under attached/separated flow conditions. The differences in rotor performance predictions between both methods are found to be small and this is attributed to the effect of slightly differing circulation distributions on sectional thrust/torque and wake data. In general, the classical Kutta-Joukowski appears to perform well even with the occurrence of modest amounts of separation.