Gurney flap effects and scaling for low-speed airfoils

Abstract

The effects of Gurney flaps were tested on two airfoil sections, the LA203A and the Gottingen 797, in a low speed wind tunnel. Lift and drag forces, wall-pressure distributions and boundarylayer thickness measurements have been carried out,. Different Gurney flap heights ranging from 0.5% to 5.0% chord have been tested in order to identify some optimal configuration of this simple, yet promising device. The results presented are for a chord Reynolds number of 250 000 and reveal, in accordance with higher Reynolds number studies, that Gurney flaps may indeed provide a significant increase in lift a t very little cost in drag. It is further shown that through the proper use of Gurney flaps, the aerodynamic performance of a simple design, easy-t,o-build airfoil can be made practically as good as those of a modern, high performance, complex design. T h e present study suggests that both the critical and the optimal height of Gurney flaps (in t,erms of the l / d ratio) scales with the thickness of the boundary-layer a t the trailing-edge of the baseline airfoil on the pressure side. Based on the results of this study and previous investigations, this conclusion appears supported over a wide range of Reynolds numbers. A preliminary discussion on the physical mechanism behind the Gurney's effects and its scaling is also proposed.

Numerical Assessment of Virtual Control Surfaces for Load Alleviation on Compressor Blades

“…Additionally, the light reductions of drag coefficient relative to the clean blade-encountered with both pressure and SS actuation-are in agreement with other results found in literature on trailing edge devices (see e.g., Refs. [16][17][18][19][20]49]). It is also worth remarking that the present fully-turbulent RANS assessments can't provide a quantitative evaluation of drag.…”

Optical-velocimetry, wake measurements of lift and induced drag on a wing

“…Surface pressure measurements [16,17,20] have shown that the increase in lift coefficient was caused by the Gurney flap increasing both the peak suction and the trailing edge loading. Moving the Gurney flaps forward from the trailing edge did not eliminate this effect [17].…”

Comparison of Aerodynamic Effects Promoted by Mechanical and Fluidic Miniflaps on an Airfoil NACA 4412

“…Giguére et al [6], described experimentally the aerodynamic behavior of these flaps scaling their height with the boundary layer thickness.…”