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Saltation of uniform grains in air

Published online by Cambridge University Press:  28 March 2006

P. R. Owen
Affiliation:
Department of Aeronautics, Imperial College, London

Abstract

The interaction between a turbulent wind and the motion of uniform saltating grains of sand or soil, so massive as to fail to enter into suspension, is examined on the basis of two complementary hypotheses. The first asserts that the effect of the moving grains on the fluid outside the region to which saltation is confined is similar to that of solid roughness of height comparable with the depth of the saltation layer. The second requires the concentration of particles engaging in the saltation to adjust itself so that the shear stress exerted by the wind on the ground—different from that acting on the fluid outside the saltation layer by an amount accountable to the change in horizontal momentum suffered by the particles in their passage through the fluid—is just sufficient to maintain the sand-strewn surface in a mobile state.

Existing experimental data on the wind profiles outside the saltation region and the horizontal flux of particles through it are shown to be consistent with these hypotheses.

The second hypothesis implies a self-balancing mechanism for controlling the concentration of saltating particles. For if the concentration is too low the shear stress at the surface rises above the value required merely to secure mobility and more particles are encouraged to leave the surface; conversely, too large a concentration depresses the surface stress, and the consequent loss of surface mobility inhibits saltation and reduces th concentration of particles until equilibrium is restored.

Type
Research Article
Copyright
© 1964 Cambridge University Press

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References

Bagnold, R. A. 1936 Proc. Roy. Soc. A, 157, 594.
Bagnold, R. A. 1937 Geogr. J. 89, 436.
Bagnold, R. A. 1941 The Physics of Blown Sands and Desert Dunes. London: Methuen.
Chepil, W. S. 1945a Soil Sci. 60, 305.
Chepil, W. S. 1945b Soil Sci. 60, 397.
Chepil, W. S. 1945c Soil Sci. 60, 475.
Leliavsky, S. 1955 An Introduction to Fluvial Hydraulics. London: Constable.
Prandtl, L. 1952 The Essentials of Fluid Dynamics. London: Blackie.
Rouse, H. 1950 Engineering Hydraulics. New York: Wiley.
Schlichting, H. 1955 Boundary Layer Theory. London: Pergamon.
Shields, A. 1936 Mitt. Preusz. Versuchs. für Wasserbau u. Schiffbau, nr. 26.
Zingg, A. W. 1953 Univ. Iowa Studies in Engng Bull. no. 34.
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