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Wind Turbine Control
Published in Thomas Corke, Robert Nelson, Wind Energy Design, 2018
A variation on a split flap is a Gurney flap. This consists of a vertical fence that sits on the surface of an airfoil near the trailing edge. A schematic showing a Gurney flap at the very trailing edge of an airfoil section is shown in Figure 6.20. The Gurney flap causes a flow separation to occur upstream and downstream of the flap which changes the pressure distribution at the trailing edge, and subsequently the lift force on the airfoil. A Gurney flap on the lower surface (pressure side) of an airfoil will increase lift. This is the example shown in Figure 6.20. A Gurney flap on the upper surface (suction side) will produce negative lift. The general rule of thumb for Gurney flaps is that their height should range between 1% to 1.5% of the airfoil chord length, and that their position should be from 0% to 10% of the chord length from the trailing edge of the airfoi1[4]. The largest effect occurs when the Gurney flap is placed at the exact trailing edge. An illustration of multiple spanwise Gurney flaps for spanwise varying lift contro1[10] is shown in Figure 6.21. In this arrangement the Gurney flap segments would be extended or retracted to provide spanwise lift control.
Principles and Applications of Plasma Actuators
Published in Ranjan Vepa, Electric Aircraft Dynamics, 2020
A Gurney flap, illustrated in Figure 9.7, is small rectangular flap-like device located on the pressure side of the airfoil, towards the trailing edge, and having a width of around 1–3% of the chord. The Gurney flap increases lift produced by the airfoil, with only a small increase in drag, making it an effective, low-maintenance, high-lifting device, which was introduced in the early 70s in the racing industry to increase the downforce on the cars.
Numerical investigation of aerodynamic characteristics of naca 23112 using passive flow control technique – gurney flaps
Published in Cogent Engineering, 2023
The current paper will study the effect of gurney flaps on the aerodynamic performance of a NACA23112 reflex airfoil with a 1 m chord. The main objective of this paper is to study the effect of three different flap lengths and positions on the aerodynamic performance of the airfoil. CFD method using Ansys Fluent has been adopted for the project. The models and settings used have been validated with results from experimental studies conducted by other researchers, and mesh independence studies have been carried out. The lift and drag coefficients are reported, which are used to arrive at the aerodynamic efficiency. Further, the models are referred to as X-YY, where X is the length of the flap percentage of the chord, and YY is the position of the flap from the leading edge of the airfoil as a percentage of the chord. The following conclusions were drawn. Gurney flaps aid in increasing the lift and drag coefficients of the airfoil. This increase is related to both the height and position of the flap.With an increase in the flap height from 1% to 3% chord, the lift coefficient increases from 60% to 130%. However, the drag coefficient also increased from 52% to 153%, with the rise in flap height. A balance is thus necessary to obtain optimal performance from the Gurney flaps.Among the three positions tested, the increase in Cl varied from 125% to 135%, and the increase in Cd ranged from 153% to 140% for the configurations. The drag was less affected by the change in the position of the flap as opposed to the effect of its length.The designs’ aerodynamic efficiency (Cl/Cd) was compared to arrive at the best configuration. A 37.9% increase in Cl/Cd was obtained for the 1-100 design. This configuration also had the best efficiency throughout the entire range of angles of attack tested.The premature onset of the stall was noted due to the use of Gurney flaps. While the stall angle of the plain wing was nearly 18°, the wing with GFs had a stall angle close to 14°. However, the lift coefficient during stall was higher than the plain wing, thus resulting in better stall recovery.The pressure and velocity contours confirmed the increase in pressure on the pressure side and the delay of the point of separation of the flow on the suction side near the trailing edge. This agrees with previous findings on the flaps’ working principle.