COLLISIONAL SHEET FLOWS OF SEDIMENT DRIVEN BY A TURBULENT FLUID

We consider a sheet flow in which heavy grains near a packed bed inter act 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 turbulen t fluid and introduce what we believe to be the simplest theory for th e collisional regime that captures its essential features. We employ a relatively simple model of the turbulent shearing of the fluid and us e kinetic theory for the collisional grain flow to predict profiles of the mean fluid velocity, the mean particle velocity, the particle con centration, and the strength of the particle velocity fluctuations wit hin the sheet. These profiles are obtained as solutions to the equatio ns of balance of fluid and particle momentum and particle fluctuation energy over a range of Shields parameters between 0.5 and 2.5. We comp are the predicted thickness of the concentrated region and the predict ed features of the profile of the mean fluid velocity with those measu red 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 san dstorm and calculate profiles of particle concentration, velocity, and local volume flux.