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Potential flow theory for airfoil spoilers Jandali, Tarek

Abstract

A theory is presented for the calculation of the pressure distribution and lift for arbitrary thick airfoils fitted with normal upper surface spoilers in two dimensional incompressible flow. Airfoil shape and angle of attack and spoiler location and height are arbitrary and unrestricted. The theory uses a sequence of conformal transformations from a basic flow past a circle, with one or two sources on that part of the circle corresponding to the surface of the airfoil and spoiler exposed to the wake. The flow inside the separating streamlines is ignored, and the upper surface pressure downstream of the spoiler is taken as an empirical parameter, assumed constant. The sources in the wake permit satisfaction of Kutta conditions with the desired pressure at the spoiler tip and airfoil trailing edge. Features of the theory include good prediction of loading distribution, a finite wake width and a pressure distribution on the separating streamlines decreasing asymptotically towards the free stream value at infinity. The theoretical predictions are compared with lift and pressure measurements on a Joukowsky airfoil of 11% thickness and 2.L\% camber, and with lift measurements on a 14% thick Clark Y airfoil. Both airfoils were tested through a range of angle of attack with spoilers of 5 and 10% chord height, each at several locations. Good agreement is found.

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