A parametric study on the effect of Gurney flaps on single and multielement airfoils, three-dimensional wings, and reflection plane model

Abstract

The effect of Gurney flaps on twodimensional airfoils, three-dimensional wings, and reflection plane model was investigated. There have been a number of studies on Gurney flaps in recent years. However, these studies have been limited to two-dimensional airfoil sections. A comprehensive investigation on the effect of Gurney flaps for a wide range of configurations and test conditions was conducted at Wichita State University. A symmetric NACA 0011 and a cambered GA(W)-2 airfoils were used during the single element airfoil part of this investigation. The GA(W)-2 airfoil was also used during the two-element airfoil study with its 25% chord slotted flap deflected at 10, 20, and 30 degrees. Straight and tapered reflection plane wings with Natural Laminar Flow (NLF) airfoil sections were tested for the three-dimensional wing part of this investigation. A fuselage and engine were attached to the tapered NLF wing for the reflection plane model investigation. Compared to the baseline clean configuration, the Gurney flap improved the maximum lift coefficient. However, there was a drag penalty associated with this lift increase. c Cd Q cm Nomenclature Chord length Drag coefficient Lift coefficient Pitching moment coefficient, quarter or half chord as indicated Freestream dynamic pressure, Uw Freestream velocity x,y,z Streamwise, spanwise, normal directions a Angle of attack d Flap deflection p Freestream density Introduction The Gurney flap is a short flat plate attached to the trailing edge perpendicular to the chordline on the pressure side of the airfoil. Race car driver Dan Gurney used this flap to increase the down force and thus the traction generated by the inverted wings on his race cars. Field tests by Gurney found that the flap increased the lift (i.e., traction) while the drag was slightly decreased. Increasing the Gurney flap height beyond 2% of chord continued to Increase the lift, but at the cost of substantially increased drag. Numerous wind tunnel tests on Gurney flaps have been conducted on both single and multi-element airfoils (see Giguere et afi for an extensive list). Liebeck found that the lift was increased when a Gurney flap was attached onto a Newman airfoil. Tuft flow visualization during the experiment indicated a downward turning of the flow behind the Gurney flap. Dye flow visualization on a NACA 0012 airfoil by Neuhart and Pendergraft also showed a downward turning of the flow behind the Gurney flap. Airfoil pressure distribution measurements were taken by Robert McGhee on an advanced technology airfoil. He found that the Gurney flap produced an overall decrease in pressure on the upper surface and an overall increase in 'Assistant Professor, Senior Member AIAA. 1 Associate Professor, Member AIAA. ^Graduate Assistant, Student Member AIAA. Copyright ® 1997 by Roy Myose, Michael Papadakis, and Ismael Heron. American Institute of Aeronautics and Astronautics, Inc. with permission. Published by the