Aerodynamics of a double-element wing in ground effect

Abstract

A study was performed of a cambered, double-element, high-lift wing operating in ground effect. The effect of ground proximity and flap setting has been quantified in terms of aerodynamic performance and off-surface flowfield characteristics. Measurements include surface pressure taps, force, surface streaklines, and laser doppler anemometry (LDA). It was found from the Haw visualization that the flow is three-dimensional (3D) towards the wing tip with the main element generating most of the downforce, but retains quasi-2D features near the centre of the wing. However, at large heights the downforce increases asymptotically with a reduction in height, Then there is either a plateau, in the case of a low flap angle, or a reduction in down-force, in the case of a large flap angle. The downforce then increases again until it reaches a maximum, and then reduces at a height near the ground. The maximum downforce is dictated by gains in downforce from lower surface suction increases and losses in downforce due to upper surface pressure losses and lower surface suction losses, with a reduction in height. For the high flap angle, there is a sharp reduction just beyond the maximum, due to the boundary layer separating, and a resultant loss of circulation on. the main element.

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