Page 233 - Introduction to Naval Architecture

218 PROPULSION

Figure 9,7 Lift and drag curves

Each of these coefficients will be a function of the angle of incidence
and Reynolds' number. For a given Reynolds' number they depend on
the angle of incidence only and a typical plot of lift and drag
coefficients against angle of incidence is presented in Figure 9.7.
Initially the curve for the lift coefficient is practically a straight line
starting from a small negative angle of incidence called the no lift angle.
As the angle of incidence increases further the curve reduces in slope
and then the coefficient begins to decrease. A steep drop occurs when
the angle of incidence reaches the stall angle and the flow around the
aerofoil breaks down. The drag coefficient has a minimum value near
the zero angle of incidence, rises slowly at first and then more steeply
as the angle of incidence increases.

Lift generation
Hydrodynamic theory shows the flow round an infinitely long circular
cylinder in a non-viscous fluid is as in Figure 9.8.

Figure 9.8 Flow round circular cylinder