Page 178 - Aerodynamics for Engineering Students
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Two-dimensional wing theory 161
(a) No circulation
(b) Low circulation
(c) High circulation
(d) Circulation such that Kutta condition is satisfied
Fig. 4.1 Effect of circulation on the flow around an aerofoil at an angle of incidence
the flow leave the upper and lower surfaces smoothly at the trailing edge. This is the
essence of the Kutta condition first introduced by the German mathematician Kutta.*
Imposing the Kutta condition gives a unique way of choosing the circulation for
an aerofoil, and thereby determining the lift. This is extremely important because
otherwise there would be an infinite number of different lifting flows, each corres-
ponding to a different value of circulation, just as in the case of the spinning cylinder
* W. Kutta (1902) ‘Lift forces in flowing fluids’ (in German), Ill. Aeronaut. Mitt., 6, 133.
