Discharge Analysis of SMBF Flumes in Free and Submerged Flow Conditions

One of the most commonly used devices for flow measurements in open channels is the flume, in which the flow velocity increases due to the lateral contraction, raising the bottom of the channel, or a combination of both them. SMBF is a flume with the above mentioned properties, having two semi-cylinders on the side walls of the channel that contract the cross-sectional area of the flow. In this study, the SMBF flume has been studied for measuring the flow in free and submerged flow conditions. Using the experimental data (575 runs) of two rectangular channels, and using eight SMBF flumes, the proposed discharge equations were examined for the wide ranges of flow discharge, upstream depth, and contraction ratio. In the present study, based on the numerical and experimental analysis, and by measuring the velocity distribution at the throat section, non-uniformity of velocity distribution and depth in the contracted section, as well as the two-dimensional nature of flow were studied. Then, by considering the flow correction coefficients in the throat section and applying them into the energy equation, an equation was developed for estimating the flow discharge‎ under free flow conditions. Also, two equations were developed to determine the submergence threshold (as a function of upstream depth and throat width) and for the discharge estimation under submerged conditions. The mean absolute relative error of the estimated flow discharge of the SMBF flumes in free flow conditions and based on three experimental data series (channel 1, channel 2, and other researcher’s data) were respectively estimated to be 2.82, 3.19 and 1.52%. Additionally, the mean absolute relative error of the estimating flow discharge in the submerged conditions was 5.51%. The results showed a feasible application of SMBF structure, as a portable measuring instrument under free and submerged conditions.