Aerodynamic Analysis of a Flapping Rotary Wing at a Low Reynolds Number

Abstract

A flapping rotary wing is a novel layout for micro air vehicle design. A computational fluid dynamics method is employed to understand the unsteady aerodynamic behavior of such a layout at a low Reynolds number. A comparison of flow between an flapping wing and a typical flapping rotary wing is conducted to evaluate the effect of rotational moment. Although the mean lift of the flapping wing is close to zero, a large mean rotational moment can drive the wing to rotate. A large mean lift coefficient can be obtained when the wing begins to rotate, but the mean rotational moment coefficient starts to decrease. The leading-edge vortex is attached to the wing surface until it moves to the trailing edge, despite the negative spanwise flow near the tip. The aerodynamic force depends on nondimensional variables, including flapping amplitude, mean angle of attack, pitching amplitude, ratio of period of flapping to rotation motion , and Reynolds number. An analysis of these nondimensional variables shows that only an increase in pitching amplitude or Reynolds number increases both mean lift and rotational moment, which is an expected feature for micro air vehicle design.