Computation of Shallow Recirculating Flow Dominated by Friction

Abstract

The recirculating flow produced by a sudden widening of flow in a shallow open channel is computed using three turbulence models including (1) a constant-eddy-viscosity model; (2) a depth-averaged k -ε model; and (3) a two-length-scale model. The computational results demonstrate the existence of a friction-dominant regime. In this regime, all turbulence models give approximately the same recirculating length and the same recirculating flow rate despite the different levels of eddy viscosity determined by the models. The length of the recirculating zone obtained by the models is approximately equal to one frictional-length scale, and the recirculating flow rate equal to 2.5% of the frictional flow rate; these numerical results are in agreement with the experimental observations. The implication on the computation of the turbulent flow in natural waterways is discussed in light of these numerical results.