Aerodynamics on flapping rotary wing in low reynolds number

Unsteady aerodynamics of a flapping rotary wing with aspect ratio of 5 is studied in low Reynolds number. The effect of five different dimensionless parameters is discussed. It is shown a positive or negative leading-edge vortex is formed corresponding to the negative or positive lift during upstroke or downstroke. The leading-edge vortex attach on the wing surface until they moves to trailing-edge despite the second vortex can be observed. Based on the analysis of different Reynolds number, it is indicated that relative high Reynolds number can obtain high lift and rotational moment due to the strengthened leading-edge vortex. The decrease of flapping amplitude and the increase of the ratio of flapping period by rotation period both lead to a higher rotation rate, which increase lift and decrease the rotational moment. With the increase of mean angle of attack, a stronger leading-edge vortex occurs during upstroke, which increases lift and decrease the rotational moment. The variation of pitching amplitude changes the mean angle of attack during upstroke or downstroke, which results in the increase of the lift and rational moment.