Numerical Study of Hydraulic Performance of Weir-flume Combined Device

【Objective】 The weir-flume apparatus, consisting of a measuring flume and a measuring weir, is an innovative device for monitoring and controlling open channel flow. Installed across channels, it can measure water flow, elevates upstream water level, and enhances ecological connectivity in rivers in diverse geographical conditions. While measurement formulas and hydraulic characteristics have been experimentally investigated for small flow with shallow water depth, there is a lack of study for large flow. This paper aims to bridge this gap by studying the vertical and longitudinal velocity profiles as well as spatial distribution of flow field under high flow conditions. 【Method】 The analysis was based on numerical modelling. The FLOW-3D software was used to simulate hydraulic performance of a weir-flume device under 17 flow rates ranging from 10.13 to 200 L/s. From the simulated results we analyzed the impact of flow rate on water depth, Froude number (Fr), and velocities within both the in-groove flow and the weir flow. 【Result】 As the flow rate increased, the Fr and velocity in the central longitudinal section of the device initially increased and then tapered off. The flow in the upstream of the device remained stable, with Fr ranging from 0.1 to 0.3 and velocities varying between 0.08 and 0.5 m/s. Both Fr and velocity gradually increased with the increase in flow rate. After entering the device, Fr and flow velocity exhibited a significant surge. A wide range of thin water layers emerged in the downstream of the device, with the maximum Fr and velocities being 3 to 4.6 and 1.05 to 2.06 m/s, respectively. A subdued water jump was observed downstream of the in-groove flow, while the downstream of the weir showed a jet stream with Fr>1. Additionally, diffused water generated a rhomboid wave at the side bank. We derived a formula from the numerical simulations; its maximum relative error was 6.11% for flow rate below 100 L/s, beyond which the relative error gradually increased. 【Conclusion】 The numerical results obtained from FLOW-3D agreed well with the test data, validating the accuracy and consistency of the derived formula for analyzing measurement data from the weir-flume device. This work bridges a critical knowledge gap, enabling more precise assessment and control of open channel flow under various conditions.