The relationship between flow and pressure head of partially submerged orifice through CFD modelling using FLOW-3D

Abstract

Orifices are used as flow control and measuring devices and classified based on their sizes, shapes, and flow conditions. For partially submerged orifice, relatively few studies provide analytical results because it is highly dependent on the orifice’s geometry and the net flow head available. The purpose of this study is to determine the relationship between the flow rate and the pressure head of a circular orifice in partially submerged flow conditions using FLOW-3D software. Three cases were considered: Case A, a classical free-flowing circular orifice for validation, Case B, varying upstream and downstream water depth at weir flow conditions; and Case C, partially submerged circular orifice with varying upstream water levels and constant downstream water level at the centre of the orifice. A strong linear relation is obtained between the upstream water level and the flow rate through the orifice for Cases A and C, while the relationship remains valid for Case B unless the water depths exceed the invert of the circle downstream. The percentage of difference in weir flow past orifice between the model and equations derived from previous studies are within 20% with a regression value of 0.99 for all water level differences, except for a couple of cases with small water level differences in which the flow is very complex.