Weir velocity formulation for sharp-crested rectangular weirs

• This research is a combination of experimental and numerical study of sharp-crested rectangular weirs.
• A parameter named as weir velocity, which resembles the very basic definition of Froude number, has been substituted by discharge coefficient (Cd) for a simpler and more accurate discharge calculation.
• The mentioned type of weir was divided into slit and contracted class through a technical approach.
• CFD solution was adopted to verify the experimental results.

Discharge in open channels can be measured by sharp-crested rectangular weirs. Generally, measured head over the weir crest is substituted into an empirical formula derived from energy considerations to calculate the discharge. Assumptions made on the derivation are taken into account by defining a discharge coefficient that fits into the experimental data. In this study, a physical quantity, the average velocity over the weir section defined as ‘weir velocity’ is directly formulated as function of weir geometry and head over the weir. Weir velocity plotted against the weir head has a universal behavior for constant weir width to channel width ratio independent of the weir size. This unique behavior is described in terms of weir parameters to calculate the discharge without involving a discharge coefficient. Combining weir velocity data for variable weir widths provides a basis for direct formulation of discharge. The weir velocity exhibits simpler functional dependency on weir parameters in contrast to the discharge coefficient.