Effect of Gurney Flap Relative Span on Lift, Drag, and Trailing Vortex of a Rectangular Wing

Abstract

[Abstract] An experimental study has been conducted to examine the effects that Gurney flap span has on the lift and drag of the wing-flap configuration and the near-field trailing vortex strength. The configurations tested included a rectangular wing, a full-span Gurney flap and two Gurney flaps having spans equal to one half the wing span, one positioned outboard, and the other inboard. All three flaps had a height equaling six percent of the wing chord. As expected, all three flaps significantly changed the wing lift and drag characteristics. While the flapped configurations developed much higher both lift and drag coefficients, the overall effect on the wing lift-to-drag ratio has been found to be detrimental for all three flap configurations as compared to the baseline wing, the negative effect increasing with the flap span. Also, significant flattening of the lift-to-drag vs. lift coefficient curve has been observed. As expected, the addition of the flaps led to additional trailing vortices which affect the overall trailing vortex rollup and strength. The effect of the flaps on the trailing vortex strength in the near field has been quantified using a rollup tightness factor. This measure has indicated that while the configurations employing the full-span Gurney flap and the 50-percent-span flap located over the outboard wing sections exhibited trailing vortex strength reductions over most of the range of angles of attack tested, the configuration involving the inboard 50-percent flap developed stronger trailing vortices in the near field. These results have indicated that an effective means for trailing vortex reduction via Gurney flap use should be sought within the design space incorporating flaps located outboard. Future studies should include outboard Gurney flaps of varying relative span, other wing planforms and higher Reynolds numbers. Also, far field effects need to be examined.