Flow through Partially Submerged Orifice

Vertically mounted circular orifices have been extensively used for flow measurements. The operation of a side orifice is not always under a high headwater above the crown of the orifice, as a result, the prediction of partially submerged flow is characterized as a mixing flow between weir and orifice flows. The general equations of weir and orifice need to be tailored to predict partially submerged orifice flows. The purpose of this study is to derive a new method for calculating the discharge flow rate through partially submerged circular orifice. The method applies a weighting factor to construct a reliable rating curve for the transitional flow from a weir flow when the flow depth is shallow to an orifice flow when the flow depth becomes deep. The proposed method is further normalized in form of the Froude Number using the diameter of the orifice as the characteristic length and gravitational acceleration as the characteristic time. For engineering practices, the best-fitted orifice discharge coefficient was determined to be 0.53 using the least squared error method. (C) 2017 American Society of Civil Engineers.