Analysis of hydraulic characteristics of Subcritical flow on semi-elliptical and rectangular side weir and determining discharge coefficient using finite volume method

Side weirs are used to control the amount of discharge in main channels and rivers. One of the types of side weirs are labyrinth Semi-elliptical side weir and Due to the greater crest length in a certain range of transverse, have more the discharge capacity than rectangular weirs. For these reasons in this study, flow around a semi-elliptical and rectangular labyrinth side weir was simulated with three-dimensional modeling finite volumeand compared with laboratory measurment. The effects of increasing the flow in the main channel and the height and length semi-elliptical side weirs on flow pattern in subcritical flow conditions were studied and finally the experimental results were compared with the simulated results for rectangular side weir. Numerical results indicated that the model can predict the the flow pattern on the side weir with high accuracy .The results of the simulation showed that the effects of secondary flows in both weirs were reduced by increasing the height of the rectangular and semi-elliptical side weirs and then, the water surface profile would be more uniform and the error rate decreas. The maximum of velocity in semi-elliptical side weir is induced in the near of free surface at the end of the side weir and the discharge coefficient of semi-elliptical side weir is more than rectangular side weir.In this study an equation was offered in order to determine De-Marchi discharge coefficient for semi-elliptical side weir.This coefficient in subcritical flow conditions depends on the Froude number in the main channel, the ratio of upstream depth to the height of side weir, the ratio of upstream depth to the length of side weir and the ratio of small ellipse radius to large ellipse radius.