Later works confirmed this finding (Bloy and Durrant, 1995 Storms and Jang, 1994). This is consistent with a reduced form drag obtained at high lift coefficients using a Gurney flap. The water tunnel tests showed that the presence of the Gurney flap provoked an extension in the region of attached flow on the upper surface of the wing, with a recirculation region behind the flap. To explain the drag reduction at high angles of attack, Liebeck presented a model of the flowfield in the region of the Gurney flap, that model has been substantiated by flow visualization tests made in a water tunnel by Neuhart and Pendergraft (1988).
The Gurney flap acts as a mechanism of passive flow control. In his tests, Liebeck studied a Gurney flap of 1.25% the wing chord length, observing an increase of the lift and lift-to-drag ratio compared with the same airfoil without the flap. Later, the Gurney flap was studied by Liebeck (1978). These devices were first used by Dan Gurney, a race car driver, on a racing car wing, resulting in an increase of its maximum speed and its down force in cornering. Its size is typically 0.5% to 2% of the airfoil chord length. Miniflaps, such as Gurney flaps, are small extensions at the trailing edge of an airfoil perpendicular to its lower surface. Improved airfoil performance using a small trailing edge flap, was first reported by Liebeck (1980) from tests made on a Newman symmetric airfoil with a Gurney flap, in a non turbulent flow environment. Hence, there is a continuous need for improving the maximum lift and lift-to-drag ratio, L/D.
Improved high-lift performance can lead to increase range and payload, or decrease landing speed and field length requirements. High-lift aerodynamics continues playing an important role in the design of a new aircraft. This interest was a consequence of a search for improving aircraft low speed performance as well as for improving the design of wind turbine blades (Fuglsang et al., 1999), rotors and propellers. The performance of airfoils operating at low Reynolds numbers has been a topic of increasing attention during the last decades. The tests were performed at a turbulence intensity of 1.8% and 3.5% and at a Reynolds number of 3x10 5. The results show that the Gurney flap acts enhancing the lift coefficient of the airfoil, and that its performance is almost independent of the scales of the incoming turbulence. (2000) at the DLR, Technical University of Berlin, Germany. Lift and drag coefficients were calculated in both cases, then plotted and contrasted with low velocity laminar wind tunnel data of the HQ17 with and without miniflaps Gurney, obtained from Bechert et al. The airfoils, with and without the Gurney flap, were submitted to two different turbulent flows with the same mean wind velocity but with different turbulence structures. , ,, , Boundary layer wind tunnel experiments have been conducted in order to investigate the influence of a Gurney flap upon the aerodynamic behaviour of an HQ 17 airfoil. Laboratorio de Capa Límite y Fluidodinámica Ambiental (LACLYFA), Facultad de Ingeniería, UNLP. Lift and drag coefficients behaviour at low Reynolds number in an airfoil with Gurney flap submitted to a turbulent flow.
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