FREE-SURFACE FLOW OF HYPERCONCENTRATIONS

A mixture of fluid and solid particles with high sediment concentratio n (hyperconcentration) is described by a non-Newtonian rheological mod el incorporating the yield stress, a linear (viscous) stress, and a qu adratic (turbulent-dispersive) term. Unsteady flow of hyperconcentrati on down an inclined plane is studied: first the set of equations gover ning the flow are derived, then velocity profiles for steady uniform m otion are illustrated. The solution for unsteady state flow is obtaine d in term of permanent waves; their speed is derived and the possible surface profiles are illustrated as functions of a dimensionless param eter describing the relative importance of the linear and quadratic te rm. When the viscous stress overwhelms the turbulent-dispersive one, e arlier relations for a Bingham fluid are recovered. It is shown that m ore types of gravity currents are possible than in a Newtonian fluid; these include some cases of permanent waves propagating up a slope. (C ) 1999 The Japan Society of Fluid Mechanics and Elsevier Science B.V. All rights reserved.