Numerical modeling of flow past a side weir

Abstract

The present study focuses on hydraulics of sharp-crested side weirs and is restricted to subcritical flows over rectangular side weirs in rectangular channels. A CFD model (a finite volume based solver, STAR-CCM+) is used to simulate the flow past a side weir. A hexahedral grid with 896,112 cells is used and overset meshing capability is used to simulate a moving side gate. Realizable two layer k ?? turbulence model is used. The numerical model is validated against earlier experimental results for steady flows past side weir. Results from the steady flows are generalized to find out relations for coefficient of discharge, maximum velocity, minimum flow depth and flow division zones. The flow depth is seen to increase along the flow as is the case with subcritical flows. The steady flow streamlines indicate that the flow field is divided into two zones. Flows in the two zones are diverted towards the side weir and outlet of the main channel, respectively. Two different kinds of unsteady flows are considered, (i) by varying the weir configuration (weir length, weir height, both weir height and length) with time and (ii) by introducing a flood wave at the inlet. Results from the first kind of unsteady flow indicate that discharge corresponding to a weir size with unsteady condition is higher compared to that of steady condition. A modified coefficient of discharge taking into account the unsteady flow condition is proposed. The second kind of unsteady flow results in a relation between the peak side weir discharge and the characteristics of the flood wave.