Question

Generation of lift over an airfoil and formation of starting vortex is correctly explained by which of these?

(a) Kutta-Joukowski Theorem

(b) Kutta Condition and Kelvin’s Theorem

(c) Kutta-Joukowski Theorem and Kelvin’s Theorem

(d) Kutta Condition and Helmholtz Theorem

I got this question in a job interview.

The query is from Kelvin’s Circulation Theorem and the Starting Vortex topic in portion Incompressible Flow over Airfoils of Aerodynamics

Answer 1

The correct choice is (b) Kutta Condition and Kelvin’s Theorem

To elaborate: Kutta condition enforces smooth flow at the trailing edge. In doing so high velocity gradients formed at the trailing edge generates vorticity and hence circulation is there. From Kelvin’s circulation theorem starting vortex is formed to conserve circulation.