Aeolian transport with collisional suspension

Abstract

This paper considers the aeolian transport of sand by a wind so strong that the concentration of sand near the bed makes collisions between grains inevitable. It employs an improved model of such a collisional flow which includes turbulent suspension, viscous dissipation and new top boundary conditions that are validated by numerical calculations of collisionless trajectories.

Periodic saltation over hydrodynamically rough beds: aeolian to aquatic

“…This is no longer true when twice the height of the trajectory H is greater than the mean free path of kinetic theory, upper limit for the existence of a pure saltation regime in terms of the Shields parameter as a function of the density ratio at a given Stokes number. Above this limit, collisional suspension begins to take place (Berzi 2013, Jenkins & Hanes 1998, Pasini & Jenkins 2005. Figure 10 shows a regime map in terms of Shields parameter versus density ratio for a Stokes number of 1000.…”

“…Stronger shearing flows make inter-particle collisions above the bed probable, and these collisions provide a mechanism to sustain the weight of the particles (Berzi & Fraccarollo 2013, Jenkins & Hanes 1998, Pasini & Jenkins 2005. At even stronger shearing, the weight of the particles is counter-balanced by the mean turbulent lift -turbulent suspension (Drew 1975, McTigue 1981, Hsu et al 2003.…”

Two-Dimensional Numerical Simulation of Saltating Particles Using Granular Kinetic Theory

“…A rectangular 2D geometry was chosen with a logarithmic profile for the inlet air velocity, along with an initial amount of sand at rest in the lower part of the simulation domain, resembling the particle saltating flow commonly seen in the vertical middle plane within saltation wind tunnels. This model is validated with experimental data from Liu and Dong [2] and the results given by Pasini and Jenkins [1]. A good estimation for the particle erosion and mass flux in the saltation layer is predicted, even though the profiles of mass flux and concentration within the transport layer are very thin and lower.…”

“…Their results showed a qualitative good estimation of the solids erosion, which suggests that the Granular Kinetic Theory could be used to simulate this phenomenon with success. Jenkins and Pasini [1] extended the previous work by adding an extra term in the gas momentum equations, originating from a second averaging process (given in Hsu et al [9]) which described an additional mechanism of suspension due to turbulence effects together with the granular pressure gradient. Furthermore, Jenkins and Pasini considered a flow regime between the saltation regime and turbulent suspension regime called the collisional regime yet, at same time, they recognized that this regime had not yet been observed experimentally.…”

“…Instead, the particles are only kept alive in the saltation layer by bed-particle collisions and momentum transfer from the air stream to the particles. In any case, the saltation layer represents a dilute regime where the maximum volume fraction is around 5.10 -4 [2], indicating that the particles in saltation contribute only to the kinetic contribution to the solids viscosity and not the collisional regime like Jenkins and Hanes [8] and Jenkins and Pasini [1] suggest.…”