EXPERIMENTS AND NUMERICAL ANALYSIS OF FLOW IN THE CHANNEL BEND DOWNSTREAM OF A NEGATIVE STEP

Abstract

 The flow structures in the bend a meandering channel downstream of a negative step were investigated under the conditions with submerged jet and undular jump using laboratory experiments and three-dimensional (3D) numerical calculations. Comparison with experimental results in straight and meandering channels shows that 3D calculations using the standard k-ε model for Reynolds-Averaged Navier-Stokes (RANS) model can explain water depth distribution downstream from the step. The results of the crosssectional velocity distribution in the meandering channel downstream of the step show that the characteristics of the velocity distribution in a bend are different between a submerged jet and a undular jump. In particular, it was found that the secondary flow of the undular jump was enhanced rather than that of the submerged jet. It indicates that the strong secondary flow and accelerating bottom velocity increase the risk of riverbank erosion along the outer bank downstream of a negative step.