FLOWFIELD ANALYSIS OF MODERN HELICOPTER ROTORS IN HOVER BY NAVIER-STOKES METHOD

The viscous, three-dimensional flowfields of UH-60A and BERP rotors ar e calculated for lifting hover configurations using a Navier-Stokes co mputational fluid dynamics method, called TURNS, with a view to unders tand the importance of planform effects on the airloads. The solution scheme is essentially a free-wake method. That is, the induced effects of the wake, including the interaction of tip vortices with successiv e blades, are captured as a part of the overall flowfield solution wit hout prescribing the structure or position of the vortical wake. Howev er, the structure of the captured tip vortex is diffused by numerical viscosity. Calculated results are presented for the UH-60A and BERP ro tors in the form of surface pressures, hover performance parameters, s urface particle flow, tip vortex, and vortex wake trajectory at two th rust conditions. The results for the UH-60A model rotor agree well wit h experiments for a moderate thrust condition. Comparison of UH-60A re sults with an equivalent rectangular UH-60A blade and a high-twist BER P blade indicates that the BERP blade, with an unconventional planform , produces more thrust at a given collective pitch, and approximately the same Figure of Merit. The high thrust conditions considered produc e severe shock-induced flow separation for the UH-60A blade, while the BERP blade develops more thrust and minimal separation. The BERP blad e produces a tighter tip vortex structure compared with the UH-60A bla de. These results and the discussion presented bring out the similarit ies and differences between the two rotors.