Engelund's Analysis of Turbulent Energy and Suspended Load

Abstract

We analyze a one-equation model for the turbulent kinetic energy of an open channel flow in the presence of suspension sediment. Engelund's pioneer analysis and his criterion for the threshold conditions for the initiation of suspension are revisited, and it is concluded that such criterion does not represent any physical response of the system under consideration, but rather appears to be an artifact of the mathematical manipulations of the turbulent energy equation. The present analysis indicates that the effect of the suspended sediment on the turbulent kinetic energy near the bed is to reduce such energy when the particle size is sufficiently small, and that the reduction increases with the sediment concentration and the particle settling velocity to flow shear velocity ratio. On the other hand, suspended particles of larger size can enhance the turbulence of the flow because of the production of turbulent kinetic energy through vortex shedding mechanisms. A criterion is proposed to estimate the conditions for which turbulent enhancement due to the presence of suspended sediment occurs.