Collisional sheet flows of sediment driven by a turbulent fluid

Abstract

We consider a sheet flow in which heavy grains near a packed bed interact with a unidirectional turbulent shear flow of a fluid. We focus on sheet flows in which the particles are supported by their collisional interactions rather than by the velocity fluctuations of the turbulent fluid and introduce what we believe to be the simplest theory for the collisional regime that captures its essential features.We employ a relatively simple model of the turbulent shearing of the fluid and use kinetic theory for the collisional grain flow to predict profiles of the mean fluid velocity, the mean particle velocity, the particle concentration, and the strength of the particle velocity fluctuations within the sheet. These profiles are obtained as solutions to the equations of balance of fluid and particle momentum and particle fluctuation energy over a range of Shields parameters between 0.5 and 2.5. We compare the predicted thickness of the concentrated region and the predicted features of the profile of the mean fluid velocity with those measured by Sumer et al. (1996). In addition, we calculate the volume flux of particles in the sheet as a function of Shields parameter.Finally, we apply the theory to sand grains in air for the conditions of a sandstorm and calculate profiles of particle concentration, velocity, and local volume flux.

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.…”

SedFoam-2.0: a 3-D two-phase flow numerical model for sediment transport

“…In terms of the turbulence closure, the first one that has been tested was a mixing length model by Jenkins and Hanes (1998) followed by others (e.g., Dong and Zhang, 1999;Revil-Baudard and Chauchat, 2013). The other turbulence model that has been used is the k − ε model (e.g., Hsu et al, 2003;Longo, 2005;Bakhtyar et al, 2009).…”

Multimode Morphodynamic Model for Sediment-Laden Flows and Geomorphic Impacts

“…The thickness of the sheet-flow layer is calculated by the relationship h b =µ d 50 (Jenkins and Hanes, 1998, Pugh and Wilson, 1999, Sumer, et al, 1996, where µ is a dimensionless coefficient. …”