Hydraulic investigation and design of roof profile of an orifice spillway using experimental and numerical models

Abstract

The roof profile of an orifice spillway plays an important role in deciding its discharging capacity. The necessary requirement is that the profile should not experience excessive negative pressures and should be simple to construct. It is found from the literature that the flow through orifice spillway at the entrance does not follow an elliptical roof profile recommended by United States Bureau of Reclamation. During the regime of flow with high heads, flow separation takes place on the orifice roof profile resulting in reduced discharging capacity. It is also found that there is no specific design method available for design of orifice spillway roof profile with respect to the upstream head as well as other parameters. The main aim of the present study is to develop an equation for design of the roof profile of an orifice spillway. Computational fluid dynamics software FLUENT version 6.3.26 was used for the numerical simulations. The numerical model was verified and validated by comparing the results with the physical model. An equation for the design of roof profile was developed after analyzing the observed discharge through orifice, pressures on spillway bottom profile and upper nappe profile of an orifice spillway. The proposed equation was verified with the data which have not been used in deriving the equation. The proposed equation was also validated in terms of coefficient of discharge and pressure distribution on the bottom and roof profile with the existing data of some other real-life orifice spillways. The results are encouraging indicating that the developed equation can be used to get roof profile of an orifice spillway, which can be used at the design stage of an orifice spillway.