![]() in their investigation indicated that with increase in thickness of GF, C l is seen to decrease also zero-lift angle of attack shift is less pronounced with increasing thickness, suggesting that thicker flaps reduce the effective camber. , indicated that the saw-toothed GF could increase the lift and reduce the drag, thereby greatly improving the lift-to-drag ratio as compared to a plain GF of the same height. Similarly, investigations by Vijgen et al. investigated the effects of saw-toothed GF on airfoil aerodynamics, and found that saw-toothed flaps can make the flow around the trailing edge more three-dimensional. (a) Conventional aerofoil at moderate C l (b) Hypothesized flow near Gurney flap.Īerofoil. Flow over aerofoil with and without Gurney flap. studied the effect of mounting angle of GF on aerodynamic performance of NACA0012 airfoil and found that with increase in mounting angle C l increases as compared to cleanįigure 1. It was recommended that the flap should be submerged in the boundary layer, which was also confirmed by Li through experiments. suggested that the size of the optimum GF for the best lift-to-drag ratio is determined by the flow condition at the trailing edge at the pressure side of the airfoil. ![]() ![]() They found that the increment of lift coefficient had decreased when the GF has shifted forward away from the trailing edge, weakening the lift-enhancing effects of the flap. conducted the study to understand the effects of the mounting location of the Gurney flap on airfoil. It is evident that both lift and drag coefficients increase with an increase in the height of the Gurney flap. Liebeck from his results proposed the formation of two counter-rotating vortices downstream of the Gurney Flap ( Figure 1). He also concluded that flaps with a height of more than h = 2% C would significantly increase the drag. Liebeck also found that the flap height should be between 1% C and 2% C to maximize the aerodynamic benefits from this simple high-lift device. He found that the GF with only 1.25% chord length gave high-lift coefficient by increasing lift but also reducing drag at the same time. An experimental study was conducted by Bob Liebeck on a Newman aerofoil. Liebeck tested the device, which he then named the “Gurney flap” and confirmed Gurney’s field test results using a 1.25% chord flap on a Newman symmetric airfoil. Later, he discussed his ideas with an aerodynamicist and wing designer Bob Liebeck of Douglas Aircraft Company. Gurney was able to use the device in racing for several years before its real purpose became known. He improvised the car in 1971, which was underperforming, to the winning car (as a manager post-retirement from racing), this invention was inspired from spoilers attached to the rear of bodywork to cancel lift by certain teams in the 1950s. Its origin and usage on race car was introduced by Late Dan Gurney (1931-2018) a racing car driver, who later owned a racing car company AAR (All American Racers). Addition of Gurney Flap to enhance lift of an airfoil/wing is not a new concept to be thought of it was erstwhile originated from racing cars, but its roots can be traced back to 1935 by E. Generally its height varies between 1% - 2% of chord or inside boundary layer. The Gurney flap is a small flap (like tab in aircraft wing trailing edge), added at the trailing edge of an airfoil or wing at right angle to the pressure surface. ![]() At last, results obtained from combination of VG at leading edge and GF at trailing edge on Eppler 423 aerofoil are discussed at length. Also, effect of adding VG at the leading edge of Eppler 423 aerofoil is presented in this paper. Vortex Generators (VG) generate counter rotating vortices that allow the flow to remain attached even at high angles of attack. Eppler 423 being a highly cambered airfoil produces high lift coefficient and smoother stall and by adding the GF of various sizes the performance of Eppler 423 improves tremendously and reason for this enhanced performance and effect of size of GF are presented in this paper. In the present study, Eppler 423 airfoil is used to first understand the aerodynamics of such a highly cambered airfoil and later GF of various sizes w ere added on it to understand the change in flow dynamics achieved by adding the GF and their impact on aerodynamic parameters such as C l, C d and C l / C d. Use of GF at the trailing edge of the airfoil enhances the lift due to increase in the effective camber of the airfoil, which in turn improves the aerodynamic efficiency i.e. In the past extensive research has been carried out, to study the effect of Gurney flap (GF) on symmetric and cambered airfoil for its usage in low Reynolds number regime. ![]()
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