Kutta condition

Remarks

Example: a flat plate of chord $c$ at angle of attack $\alpha$ in a stream of speed $U$. Map the exterior of a circle conformally onto the exterior of the plate; the complex potential of the circle flow with circulation $\Gamma$ gives a flow past the plate. The velocity is bounded at the trailing edge exactly when the rear stagnation point of the circle flow sits at the preimage of the edge, which forces $\abs{\Gamma} = \pi U c \sin\alpha$. The plate also has a sharp leading edge, where the velocity stays unbounded; the condition is imposed only at the trailing edge. Non-example: the same flow with $\Gamma = 0$ goes around the sharp trailing edge, and its speed tends to infinity at the edge, so it fails the condition. At a trailing edge with a positive angle the condition makes $T$ a stagnation point; at a cusp the velocities on the two sides become equal and finite.