Numerical Analysis of Three-Dimensional Turbulent Structure and Secondary Flow in Trapezoidal Open-Channel Flows Using Algebraic Reynolds Stress Model.

Abstract

An investigation of turbulence structure with the secondary flow of the second kind in a trapezoidal open channel is very important in basic hydraulics and river engineering. In this study, a numerical analysis has been carried out to develope turbulent flow in a trapezoidal open channel with three kinds of bank angle. An algebraic Reynolds stress model coupled with a boundary-fitted coordinate system was abopted in order to predict Reynolds stresses precisely. Calculated results were compared with the experimental data available. It has been pointed out from the experiment that velocity-dip, which means that the maximum velocity appears not at the free surface but rather just below it, is not observed in a trapezoidal open channel. The calculated results of streamwise velocity show that the maximum velocity exists at the free surface. For this reason, the present method predics this feature. Furthermore, the secondary vectors of the calculated result are in good agreement with those from the experiment, which proves the validity of the present method. Near the free surface, the secondary flow direction in a trapezoidal open channel is opposite to that in a rectangular open channel. The orign of this difference between the cross sections is examined by evaluatidng the production term of the streamwise vorticity equation.