COMPUTATION OF SHALLOW RECIRCULATING FLOW DOMINATED BY FRICTION

The recirculating flow produced by a sudden widening of flow in a shal low open channel is computed using three turbulence models including ( 1) a constant-eddy-viscosity model; (2) a depth-averaged k-epsilon mod el; and (3) a two-length-scale model. The computational results demons trate the existence of a friction-dominant regime. In this regime, all turbulence models give approximately the same recirculating length an d the same recirculating flow rate despite the different levels of edd y viscosity determined by the models. The length of the recirculating zone obtained by the models is approximately equal to one frictional-l ength scale, and the recirculating flow rate equal to 2.5% of the fric tional flow rate; these numerical results are in agreement with the ex perimental observations. The implication on the computation of the tur bulent flow in natural waterways is discussed in light of these numeri cal results.