Modeling of Hovering Intermeshing Rotor Using Blade Element Momentum Theory

Abstract

This paper intends to establish a blade element momentum theory (BEMT) model for analyzing the rotor-and-rotor interference in the hovering intermeshing rotor system. The model uses the blade tip/hub losses to portray the intrinsic three-dimensional rotor aerodynamic effects and introduces the skew downwash flow to determine the rotor-and-rotor interference. Then, the model employs the interference locus considering the intersecting angle and the rotor hub spacing to distinguish the interference operating region on the rotor disk. Next, the BEMT model results are validated against experimental data of the German Autonomous Rotorcraft for Extreme Altitudes (AREA) helicopter and the computational fluid dynamics simulation results of the JZ series helicopters. Moreover, the effects of the rotor performance on the intersecting angle are also considered. It is found that the interference operating region resembles a semi-ellipse shape on the intermeshing rotor disk, which is not sensitive to the collective pitch angles under given structural parameters. Second, the emerging thrust recovery region created by raising the intersecting angle from 20 to 30 deg has a limited enhancement to the rotor thrust and the rotor performance. However, the incremental intersecting angle will produce a significant variation of the rotor thrust in the horizontal component in the body coordinate system, providing a large design numerical margin for the lateral stability in the hovering intermeshing rotor system.