Magnus Effect

Magnus effect

Generation of a sidewise force on a spinning cylindrical or spherical solid immersed in a fluid (liquid or gas) when there is relative motion between the spinning body and the fluid. Named after Heinrich Gustav Magnus (1802–1870), who first investigated the effect experimentally in 1853, it is responsible for the curved trajectory of a tennis or golf ball and affects the path of an artillery shell.

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Magnus effect [′mäg·nəs i‚fekt]

(fluid mechanics)

A force on a rotating cylinder in a fluid flowing perpendicular to the axis of the cylinder; the force is perpendicular to both flow direction and cylinder axis. Also known as Magnus force.

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Magnus Effect 

the appearance of a transverse force acting on a body that is rotating in a liquid or gas flow incident on it. It was discovered in 1852 by the German scientist H. G. Magnus. For example, if a noncirculatory flow passes around a rotating, infinitely long circular cylinder perpendicular to its generatrices, then because of fluid viscosity the flow velocity increases on the side where the direction of the flow velocity and the rotation of the cylinder coincide and decreases on the side where they are opposite. Consequently, the pressure increases on one side and is reduced on the other—that is, a transverse force appears; its magnitude is determined by the Zhukovskii theorem. An analogous force also occurs when a flow encounters a rotating sphere. This accounts for the nonrectilinear flight of a spinning tennis or soccer ball. The transverse force is always directed away from the side of the rotating body on which the direction of rotation and the flow are opposite and toward the side on which the directions coincide.

The Magnus effect was used in 1922-26 by the German engineer A. Flettner in constructing a rotor ship with rotating cylinders (wind-driven towers) instead of sails. In a crosswind a force that thrusts the ship acts on the cylinders. However, such ships were not used because they were not economical.

REFERENCES

Prandtl, L. Gidroaeromekhanika, 2nd ed. Moscow, 1951. (Translated from German.)
Khaikin, S. E. Fizicheskie osnovy mekhaniki. Moscow, 1963.