10 PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL
Cp
+
1.0
0
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┃ ┃
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┃~ 0 180o I ┃
┃ al ┃
┃ \ ┃
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Supcrcritical
Fig. 1.10 Schematic pressure distribution o'ver circular cylinder.
Fig. 1.11 Schematic illustration of swing of cricket ball
REVIEW OF BASIC AERODYNAMIC PRINCIPLES
11
on the top surface, the fiow separation is turbulent because of the transition caused
by the "seam," which trips the local laminar boundary layer, causing a transition to
turbulent fiow whereas, on the bottom surface, the flow separation is laminar. As a
result, the pressure distribution is asymmetric, and the cricket ball develops a net
upward force as shown. If the ball is so oriented that the whole pict,ure is rotatecl
by 90 deg, the ball develops a cross force, which will make the ball swing inward
or outward with respect to the batsman, depending on the orientation of the seam.
1.3 Drag of Bodies
The total drag of bodies exposed to airstream at low speeds consists of 1) skin
friction, 2) pressure drag, and 3) induced drag. Induced drag is also called drag
due to lift. Whereas the contributions to skin friction and pressure drag come from
all parts exposed to the airstream, contributions to induced drag come only from
lifting surfaces. At low speeds, contr:ibutions to lift come mainly from wing and
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