Study on the applicability of four flumes in small rectangular channels

Abstract

Different experiments and numerical simulation research were carried out in order to explore the hydraulic characteristics and applicability of the cutthroat flume, NACA airfoil-shaped flume, airfoil pillar-shaped flume, and optimized airfoil-shaped flume in rectangular channels. The four flumes with contraction ratios of 0.4, 0.5, and 0.6 in rectangular channels were tested under 144 free-flow conditions. Based on the Fluent software, standard k-ε three-dimensional turbulence model and volume of fluid (VOF) method were utilized for numerical simulation in each working condition. The principle of critical flow was used to analyze the correlation between the discharge, the contraction ratio, and the upstream water depth. This correlation was used to obtain the discharge calculation formulas of the cutthroat flume, NACA airfoil-shaped flume, airfoil pillar-shaped flume, and optimized airfoil-shaped flume in rectangular channels. The Froude number in front of the flume, the backwater height, the critical submergence degree, the velocity distribution, the head loss, the discharge measurement formula, and the accuracy were studied and compared. It can be concluded from the results that the cutthroat flume, NACA airfoil-shaped flume, airfoil pillar-shaped flume, and optimized airfoil-shaped flume all have good applicability in rectangular channels. Moreover, the hydraulic characteristics of all the four flumes meet the water measurement specifications in the irrigation area. The upstream Froude number of the NACA airfoil-shaped flume is the smallest, whereas the backwater height and head loss of the cutthroat flume and optimized airfoil-shaped flume are the smallest. It is also worth noting that the critical submergence degree of the optimized airfoil-shaped flume is the highest, with an average value of 0.85. The discharge measurement formulas of the four flumes have been deduced using the correlation between the discharge, the contraction ratio, and the upstream water depth. It was found that the average errors between the calculated discharge and the measured discharge of the four flumes are 3.17%, 2.17%, 1.53%, and 2.29%, respectively, which are less than 5%, and therefore meet the discharge measurement requirements. In the agricultural irrigation system and flow monitoring system, the hydraulic characteristics of the four flumes can provide a reference and basis for the selection of flumes in the rectangular channel.