Magnus effect


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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.

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.

Magnus effect

Magnus effectclick for a larger image
Lift created by spinning cylinder.
The effect on a spinning cylinder or sphere moving through the fluid, in which a force acts perpendicular to the direction of the spin. As applied to aeronautics in experimental wing forms, the Magnus theory states that if air is directed against a smooth, revolving cylinder, whose circumferential speed is greater than that of the air current, a force is directed against one side of the cylinder—air compressed on one side and vacuum formed on the other—creating lift. Named after physicist Heinrich Gustav Magnus (1802–1870).
References in periodicals archive ?
Rae's computer simulations suggest that this motion introduces an additional aerodynamic force, known as the Magnus effect, that essentially cancels out a football's tendency to drift to one side during its flight.
The phenomenon, which fluid dynamicists call the Magnus effect, can send a ping-pong ball curving up, down, left, or right - always at a right angle to the direction of motion - depending on which way the ball is spun.
Here, the thinner atmosphere reduces an object's air resistance and weakens the Magnus effect, causing a ball with top spin to travel farther than it would at sea level, says environmental fluid mechanics expert Jorge Escobar, an assistant professor at Javeriana University in Bogota, Colombia, and a competing table tennis player for 15 years.