Submergence Effects on Discharge Coefficients for Rectangular Orifices

Numerous studies have been performed to determine the discharge coefficient for orifices. These studies have included a variety of shapes, sizes, and configurations. The values developed typically ranges from about 0.6 to 0.85. However, specific discharge coefficient values for a particular configuration often appear contradictory. This is probably a result of variations in testing methods and operating conditions. The effect of submergence is also not specifically identified as a parameter for determining the discharge coefficient. Therefore, it is difficult to confidently select a discharge coefficient value from the available literature for an orifice operating under different levels of submergence. For this reason, a physical model was constructed at the Iowa Institute of Hydraulic Research to determine the effect of submergence on a rectangular orifice with partially suppressed contractions. The model results demonstrated that the discharge coefficient varies from about 0.6 to 0.85 depending on the magnitude of the submergence.