RANS COMPUTATIONS OF MILD CURVED OPEN CHANNEL FLOWS FOCUSING ON AN OUTER-BANK CELL

Abstract

A curved open channel flow is characterized by formations of cross-sectional secondary currents. The main structure of the cross-sectional flow is classified into the secondary current of 1st kind, which is caused by the centrifugal force. The outer-bank cell is generated near the corner between the surface and the outer-bank. Though the scale of the outer-bank cell is much smaller than the main secondary current, the outer-bank cell affects the erosion of the outer-bank. The previous studies showed that the outer-bank cell is initiated by two combinational effects, i. e., turbulence an-isotropy and the centrifugal force. Therefore, the criterion of the outer-bank cell is rather complicated. In this study, linear and non-linear k-E models are applied to the mild curved open channel flows studied experimentally by Booij (2003) . Only non-linear models could capture the outer-bank cell and could reproduce velocity and Reynolds stress profiles well. A 3rd order non-linear model slightly improved the accuracy. The computations with different curvature radiuses indicate that the linear k-E models can also generate the outer-bank cell in cases of very sharp bend. The threshold of R/H by the standard model for generation of the outer-bank cell was 22. The model with lower eddy viscosity could yield the outer-bank cell in the flows with larger R/H.