The effects of dynamic-stall and parallel BVI on cycloidal rotor

Purpose - This paper aims to investigate the mechanisms lying behind the cycloidal rotor under hovering status. Design/methodology/approach - Experiments were conducted to validate the numerical simulation results. The simulations were based on unsteady Reynolds-averaged Navier-Stokes (URANS) equations solver and the sliding mesh technique was used to model the blade motion. 2D and 2.5D simulations were made to investigate the 3D effects of turbulence. The effects of pressure and viscosity were compared to study the significance of the blade motion on force generation. Findings - The 2.5D numerical simulation cannot produce more accurate results than the 2D counterpart. The pitching motion of the blade results in dynamic stall. The dynamic stall vortices induce parallel blade vortex interaction (BVI) upon downstream blades. The interactions between the blades delay the stall of the blade which is beneficial to the thrust generation. The blade pitching motion is the dominant contributor to the force generation and the turbulence is the secondary. Strong downwash in the rotor cage varied the inflow velocity as well as the effective angle of attack (AOA) of the blade. Practical implications - Cycloidal rotor is a propulsion device that can provide omni-directional vectored thrust with high efficiency and low noise. To understand the mechanisms lying behind the cycloidal rotor helps the authors to design efficient cycloidal rotors for aircraft. Originality/value - The authors discovered that the blade pitching motion plays primary role in force generation. The effects of the dynamic stall and BVI were studied. The reason why cycloidal rotor can be more efficient was discussed.