Lift enhancement by Gurney – flaps

Gurney – flaps on the trailing edge of a SCCH – model (SCCH = Swept Constant Chord Half – Model) in the wind tunnel . Left: wing with 2D – Gurney – flap Right: wing with slit Gurney- flap

Drag reduction by Gurney – flaps as passive means for flow control.

Gurney-flaps are small, down bent trailing edges of airfoils presenting an effective measure for lift augmentation. Gurney – flaps can also be used for controlling the load distribution of airfoils. Typical dimensions for Gurney-flaps heights are only 1% of the chord length. The small, down bent trailing edges of airfoils present an effective measure of lift augmentation. More important applications of these modified trailing edges are to be seen on turbo machines. At wind turbines, performance increases are already reached using Gurney –flaps.

The associated parasitic drag of these trailing edges can be reduced by passive flow control. By stabilising the wake flow with passive methods a drag and noise reduction is reached. Different types of three dimensional trailing edge configuration e.g. slots, holes or vortex generators have been tested successfully. In addition a partly filling of the wake flow with a streamlined body has been tested successfully too.

For experimental tests on airfoils a wind tunnel with a test section of 1.4m x 2.0 m and a maximum speed of 40 m/s is available. Reynolds numbers of Rechord = 1x106 can be reached for an airfoil. The angle of attack variation, the data acquisition of the wind tunnel balance and the measurement of dynamic pressures and speeds respectively in the wind tunnel are controlled and evaluated by a measuring computer.

Polar of laminar profile HQ17 with different Gurney – flaps