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Gurney flaps in sailing, do they help?

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6 because in this manner the pressure recovery demand reduces. Loose relationships seem to reveal that increasing the height of the Gurney flap increases the trailing edge suction while the opposite happens if wing incidence decreases. About the trailing edge pressure, the chordwise pressures clearly show that the Gurney flap increases the pressure at the trailing edge of the airfoil because the upstream face of the flap decelerates the flow. For a flat plate immersed in a turbulent boundary layer, Good and Joubert [4] say that the maximum pressure measured upstream of the plate increases as the height of the disturbance is increased but these effects do not scale directly with the height of the device. Because the bigger Gurney flaps cause a relatively large increase in pressure, they work just as a bluff body in a ground plane that decelerates the flow which separates at some point upstream of the trailing edge, then reattaches at an other point on the upstream face of the body. The Gurney flap introduces a pressure difference acting at the trailing edge of the airfoil and it is this that generates an increase in loadings over the entire airfoil. This one can be modelled in a simple two dimensional model by modifying the Kutta-Joukowski condition. In fact the increase in suction surface velocity and the reduction in pressure surface velocity can be treated theoretically, as a vortex point placed at the trailing edge which will increase the total circulation hence the lift acting on the wing. One the nature and the physic of the phenomenon have been explored, the next step is inspecting the latest studies about the performances and the effectiveness of the Gurney flaps. Bao et al. [5] have presented a research concerning the power and efficiency augmentation of an horizontal axis wind turbine system by adding small flaps to its blades. NACA62 2 -215 was selected as the airfoil to be tested and the Reynolds number was fixed at 2.4×10 5 based on airfoil chord. The angle of attack varied from 0° to 40° and the heights of the flaps was 1.0%, 1.5%, 2.0% and 2.5% of the airfoil chord. The effects of different deflection angles

Anteprima della Tesi di Floriano Bonfigli

Anteprima della tesi: Gurney flaps in sailing, do they help?, Pagina 6

Tesi di Laurea

Facoltà: Ingegneria

Autore: Floriano Bonfigli Contatta »

Composta da 151 pagine.

 

Questa tesi ha raggiunto 1595 click dal 12/07/2004.

 

Consultata integralmente 2 volte.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.