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

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.