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The Magnus effect
By the principle outlined above, it follows that any object rotated so as to produce a vortex or circulation, will generate lift when placed in a stream of air. This is known as the Magnus effect. Figure 1.12 shows streamline patterns for air flow past a rotating cylinder.
It is possible to generate a very large amount of lift by using a rotating cylinder or paddle, but the mechanical complexities of such a system normally outweigh any potential advantages. Despite considerable interest, and many patents, the effect has rarely been exploited for commercial advantage, except by professional sportsmen; most noticably, tennis players, who use the principle to swerve a ball by imparting a large initial spin.
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Fig. 1.12 Flow past a spinning cylinder Flow is from right to left. There are several similarities between this flow, and that over a lifting aerofoil. Notice the upwash at the front, and the downwash at the rear. If the cylinder had completely spanned the tunnel, the upwash and downwash would be about equal (Photo courtesy of ENSAM, Paris) |
