Some Insights on Flow over Sharp-Crested Weirs Using Computational Fluid Dynamics: Implications for Enhanced Flow Measurement

Abstract

This study reexamines flow over a sharp-crested weir using computational fluid dynamics (CFD) to identify the optimal operating range under which the weir functions with accuracy as a free-flowing measurement device. A numerical parametric study was conducted for two separate channel and weir geometries under a range of flow rates resulting in different h/P values, where h is the elevation head over the weir crest, and P is the weir height. Analysis of velocity and pressure profiles over the weir revealed three distinct flow regimes: a high acceleration regime, an ideal operating regime, and a weir-inundated regime that may lead to submerged flow. The high acceleration regime correlates to flows with h/P<0.6, and the weir-inundated regime occurred when h/P>2.0. The ideal operating regime was found to occur in the range 0.6<h/P<2.0, where flow rate estimates using measurements of h are enhanced. These results are also consistent when considering how the discharge coefficient for the weir rating equation changes with h/P and highlight the need for caution in using empirical discharge coefficients over a broad range of h/P values.