On the Use of Coanda Effect on Truncated Airfoils, or the Jet-Flap Issues Revisited

Research associated with supercirculation concentrated on the increase of lift as a function of the momentum input while often neglecting the thrust recovery. Davidson postulated in the mid nineteen-fifties that in the presence of cross-flow the entire jet momentum must be recovered as thrust irrespective of the jet injection angle. It implies that jet tares should not be taken in wind tunnel tests and the total momentum input should be added to the drag of an airfoil. The current tests validated Davidson’s theorem using a truncated NACA-0015 airfoil with a stubby cusped flap that controlled the jet injection angle. The proof relied on a careful calibration of the jets emanating from different slot sizes and injected into stagnant surrounding fluid at angels varying from 20° to 80° prior to the introduction of the free stream. Total thrust was recovered once the input level overcame the drag generated by the stubby airfoil and a curved jet sheet was established in the test section. Most of the tests were carried out at Reynolds number of 2*105 with exit jet velocities whose Mach Number was less than 0.35. Further test focusing on potential decoupling between lift and thrust are planned.