Saltation of uniform grains in air

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.

Aeolian sand transport: a wind tunnel model

“…Most theoretical models attempt to relate transport rate to wind shear velocity or threshold shear velocity based on the momentum transfer between moving sand particles and airstream (e.g. Bagnold, 1941;Zingg, 1953;Owen, 1964;Lettau and Lettau, 1978). Theoretical models often contain some empirical coefficients that need to be determined by field observation or wind tunnel tests.…”

“…This type of equations have relatively sound theoretical support but a very severe limitation that they output meaningless sand transport when the shear velocity is less than the threshold. To overcome this drawback, the threshold shear velocity is included in the modified Bagnold-type equations (Kawamura, 1951;Owen, 1964;Iversen et al, 1976;Kind, 1976;Maegley, 1976;Lettau and Lettau, 1978;White, 1979). In fact, Bagnold's equation also has an implicit threshold term that makes the equation used only when the sand is moving.…”

“…Ever since, many successors have attempted to evaluate the previous or develop new models. Consequently, many models have been published (Kawamura, 1951;Zingg, 1953;Kuhlman, 1958;Owen, 1964;Kadib, 1965;Hsu, 1971;Kind, 1976;Maegley, 1976;Radok, 1977;Lettau and Lettau, 1978;Nakashima, 1979;Takeuchi, 1980;Horikawa et al, 1984;Sarre, 1987;Sherman and Hotta, 1990;Werner, 1990;Sherman et al, 1998). All of the published models are based on a set of ideal conditions.…”

Periodic saltation over hydrodynamically rough beds: aeolian to aquatic

“…This regime, called saltation, is the primary mode of transport in Aeolian sand transport, and has been investigated theoretically (Bagnold 1941, Bagnold 1966, Owen 1964, Ungar & Haff 1987, Sauermann et al 2001, Andreotti 2004, Jenkins et al 2010, experimentally (Bagnold 1941, Nalpanis et al 1993, Foucaut & Stanislas 1997, Iversen & Rasmussen 1999, Ho et al 2014) and numerically (Anderson & Haff 1988, Kok & Renno 2009). More references can be found in recent reviews on Aeolian transport (Durán et al 2011, Kok et al 2012, Valance et al 2015.…”

Wind erosion of sand placed inside a rectangular box

“…Owen, 1964;Nalpanis et al, 1993;Nishimura and Hunt, 2000;Liu et al, 2006), most of them relating flow properties with the erosion rate, and admitting maintenance of flat bed geometry. On the contrary, Beyers et al (2004), using a CFD code, simulated the transient three-dimensional turbulent flow of snow drifting around a cube obstacle, considering both the entrainment and accumulation, and the consequent bed-layer modification.…”