Analysis of flow-induced performance change of cycloidal rotors: Influence of pitching kinematic and chord-to-radius ratio

Abstract

As a new type of the propulsive devices, cycloidal rotor has been attracting more attention recently. The present work concentrates on the analysis of the performance and internal flow field of a two-bladed cycloidal rotor operating at low Reynolds numbers, with special emphasis on understanding how the flow structure affects the performance at different working conditions. The symmetrical/asymmetrical pitching motions are evaluated initially and the primary results show that the asymmetrical pitching with a mean pitching angle of 5◦ improves the efficiency of the rotating system. Then, the effect of the chord-to-radius ratio at three different conditions is discussed, which shows that the chord-to-radius ratio of 0.45 is the best value to maximise the performance. The flow pattern, involving the blade-wake interaction, wake-wake interaction, three vortex structures on the blade surface, roll-up vortices inside the laminar boundary layer, separation bubble, leading-edge vortex, trailing-edge vortex and flow separation vortex, are discussed in detail under various operating conditions. The study on the performance of a single blade, the forces (lift and drag) distributions, the blade loadings and the near-wall flows on two blades, provide a new understanding of the global performance change of the propeller.