Characteristics of Hydrofoil Weirs

The symmetric Joukowsky profile is investigated for its performance as a weir profile both under free flow and submerged flow conditions. The discharge coefficient is found to be a function of head and eccentricity factor, which defines the weir geometry. The discharge coefficient increases with profile thickness and crest curvature. The boundary layer effects on this particular weir coefficient are very small. The discharge coefficient is found to be about 15 to 20% higher (on average) than the conventional rectangular broad-crested weir. Under submerged flow conditions, the thinner hydrofoil weirs are found to possess a higher submergence limit (80% and more), which varies with head. The discharge reduction factor for a given submergence is found to be smaller than that of a Crump Weir. The overall performance of hydrofoil weir is found to be superior and is therefore recommended for flow measurement in open channels.