Author(s): Matthieu Dufresne; Jose Vazquez
Keywords: Critical flow theory; discharge; head–discharge relationship; measurement; open-channel; Venturi flume
Abstract: Venturi flumes are used in open-channels to determine the discharge by the measurement of a water level. The head–discharge relationship of such measurement devices can be determined following the critical flow theory, but this approach is only valid if the length of the throat is sufficiently long. Based on numerical simulations, this study determines the limit of application of this traditional critical flow theory. A discharge coefficient is introduced to take account of the effect of slope and curvature of the streamlines on the head–discharge relationship when the throat is short. An analysis of the different factors affecting this coefficient is provided. An empirical equation is proposed to evaluate this coefficient as a function of the upstream energy head, the length of the throat, the breadth of the throat and the radius of curvature of the inlet arc-shaped constriction. This correction is valid up to a deviation of 8% compared with the traditional approach and can be used in engineering practice.