Numerical Simulation of the Maximum Bottom Velocity in a Stilling Basin with a Step-down Floor

Stilling basin with step-down floor, developed from traditional stilling basin, is set up a certain height step at the initial section of stilling basin to make the high speed current away from bottom plate, and reduce the bottom velocity to protect the stilling basin board, and to ensure the project security of operation. Therefore, the maximum bottom velocity is one of the key hydraulic characteristics in stilling basin with step-down floor. This study investigates the relationship among the maximum bottom velocity, step height and flow depth and velocity on the step by applying a two-phase flow numerical simulation that combines the renormalization group k-ε turbulence model and the volume of fluid method. Simulation results show that the maximum bottom velocity does not change with the Froude number on the step under certain conditions during which step height and flow depth on the step are variable. Fitting curves are established based on the dimensionless parameter of reattachment length/step height and step height/flow depth on the step.