Experimental study on flow measurement performance of triangular flume

In view of complex shape and difficult construction of existing U-shaped channel flumes, a simplified triangular flume was designed by improving parabolic throat flume．To test flow measurement performance of triangular flume, five kinds of flumes with different contraction ratios were built on two types of U-shaped channels for irrigation area experiments．Flow measurement performance indexes were analyzed, such as flow measurement accuracy, critical submerged criterion, Froude number, and backwater height．Contraction ratio selection and construction methods for flume were discussed．Results showed that flow formula including channel gradient had an average relative error of 1.82%, with 94% of relative errors falling within ± 5%．Critical submerged criterion for triangular flumes ranged from 0.85 and 0.91, and a critical submergence formula capable of identifying flumes' free outflow state was established．Under reasonable contraction ratio conditions, both Froude number and backwater height met requirements．Contraction ratio should be primarily selected according to channel gradient's size, with flume length appropriately reduced．Then, free outflow state of measuring flume should be verified, ensuring that Froude number was less than or equal to 0.5 at minimum flow, and channel water does not flooding at maximum flow．Steel formwork method for constructing measuring flume was easy to implement without requiring breaking up original channel．Triangular flume had good flow measurement performance and could be used for flow measurement in U-shaped channels within irrigation areas．