The effects of advance ratio and blade number on the forward flight characteristics of cycloidal rotor

Abstract

Cycloidal rotor is a rotor whose blades pitch around the pitching axis and revolve around the rotor shaft that is parallel to blade. It can generate omni-directional thrust with high efficiency. In this paper, the numerical simulation models were validated by the wind tunnel experiments. Then physics of the cycloidal rotor in forward flight was studied. The effects of blade number and advance ratio were qualitatively discussed based on the numerical simulation results. Results of the analysis indicate that the rotor with more blades will result in smoother force curve, so that there will be lower vibration. However, the rotor with three or four blades will be the most efficient. The maximum forward flight efficiency is obtained from medium-to-high advance ratio. The efficiency is comparable with that of a screw propeller at the same Reynolds number. At low advance ratio, the peak lift on the blade can be observed when the blade is located at the lower left part of its trajectory. This is caused by positive blade pitch angle and relatively large inflow speed, which is similar to the downwash in the rotor cage under hovering status. From medium-to-high advance ratio, the thrust and lift primarily originated from the plunging motion of the blade. If the advance ratio is high enough, there will be negative horizontal force and positive torque, which means that the blade is taking energy from the inflow. Resultant force of the horizontal and vertical force does not vary too much with the advance ratio. But with the advance ratio approaching 1.0, the direction of the resultant force will point upwards and no horizontal force can be observed.