On the aerodynamic effects of pitching phase angle on a two-dimensional hovering wing

This paper reports a fundamental investigation of the effects of pitching phase angle on the aerodynamics of a two-dimensional (2D) flapping wing executing simple harmonic motion in hovering mode. Direct force measurement and digital particle image velocimetry (DPIV) were employed to obtain the time-dependent aerodynamic forces acting on the wing and the associated flow structures, respectively. Six pitching phase angles, i.e. 0°, 60°, 90°, 110°, 150° and 180°, were studied. For the present set of wing motions, the delayed pitching (i.e. φ <; 90°) caused the averaged lift to decrease and the averaged drag to increase, overall reducing the lift to drag ratio greatly. On the other hand, the advanced pitching, in the range of 90° <; φ ≤ 110°, caused the lift to increase and drag to decrease, resulting in higher lift to drag ratio. But further increase in the phase angle had the opposite effects, resulting in both the lift and lift to drag ratio peaking at φ ≈ 110°.