Study On The Hydraulic Characteristics And Flow Measurement Accuracy Of Parshall Flume Under Different Working Conditions

Object:As the most widely used measuring flume in Xinjiang,the Parshall flume has advantages such as low head loss and low upstream water intrusion.However,in production practice,there are still some working conditions with poor flow measurement accuracy.Therefore,exploring the applicability theory of the Parshall flume is conducive to improving the water measurement accuracy in practice.The three common channels in irrigation areas are trapezoidal channels,rectangular channels,and U-shaped channels.At the same time,the sediment content of rivers in Xinjiang is high,and there is siltation in the water delivery in the irrigation area.So this article is based on the above three channels for research,while considering the accuracy analysis of flow measurement in the case of sediment inflow.Methods:This article uses a combination of Fluent fluid simulation and physical experiments to research the hydraulic characteristics,sediment discharge capacity,and flow measurement accuracy of the Parshall flume in trapezoidal channels,rectangular channels,U-shaped channels,flow ranges of 5L/s to 80L/s,slopes of 0.1%to 0.8%,and average sediment concentration of 2.2kg/m~3.The main research content and results of this article are as follows:Results:(1)Through a 1:1 physical model experiment,the hydraulic characteristics and flow measurement accuracy of the Parshall flume were analyzed under three different channels,different flow rates,different slopes,and sediment inflow conditions.The flow measurement accuracy of the Parshall flume:trapezoidal channel>rectangular channel>U-shaped channel.In U-shaped channels,the distribution of flow velocity is relatively chaotic and uneven,with the highest Froude number observed at the well logging upstream of the Parshall flume.The Froude number at the logging point upstream of the Parshall flume under the trapezoidal channel is the smallest and the flow pattern is the most stable.Overall,as the flow rate increases,the head loss gradually increases;As the slope increases,the head loss gradually increases.The Parshall flume has a good sediment carrying capacity,and the sediment carrying capacity in most parts is greater than the average sediment concentration.There will be no sedimentation phenomenon in the flume body.(2)Based on fluid volume multiphase flow model(VOF),RNG k-εThe double equation turbulence model and PISO transient algorithm were used to calculate and simulate the clear water field experiments under different operating conditions in the Parshall flume.The simulation results are highly consistent with the experimental results,with a relative error of less than 5%.Analyze the distribution of cross-sectional flow velocity,turbulent kinetic energy,and turbulent kinetic energy dissipation rate of the Parshall flume under different operating conditions.The flow line of the trapezoidal channel is the smoothest,while the flow line of the U-shaped channel fluctuates the most violently,causing chaos and greater curvature at the inlet of the upstream connection section,resulting in relatively unstable flow patterns;The turbulent kinetic energy in the upstream of the trapezoidal channel and the contraction section of the Parshall flume is relatively small,mainly present at the gas-liquid interface and the bottom of the Parshall flume inlet.The energy exchange and transfer between molecules in the U-shaped channel are strong,and the distribution of turbulent kinetic energy is chaotic,and the turbulent kinetic energy at the bottom of the Parshall flume is greater;The turbulent flow energy dissipation rate in the upstream and connecting sections of the Parshall flume under the trapezoidal channel is the smallest.(3)Based on Euler multiphase flow model,RNG k-εThe dual equation turbulence model,Wen and Yu fluid solid exchange model,and Coupled algorithm were used to simulate three-phase flow in the water and sand fields of the Parshall flume under different operating conditions.The relative error between the simulation results and the experimental results shall not exceed 5%.The sediment distribution along the three channels and the Parshall flume under different working conditions,and the vertical distribution of suspended load concentration on the cross section are analyzed.The trapezoidal channel has the least sediment accumulation in the Parshall flume,while the U-shaped channel has the most sediment accumulation.The sediment concentration of suspended load at each section of the Parshall flume:U-shaped channel>rectangular channel>trapezoidal channel,where the sediment concentration of suspended load is greater,it is concentrated in the middle and lower part of the water level.Conclusion:It is recommended that in practical design,the water level of the Parshall flume should be maintained above 30%of the maximum water level to avoid falling below 15.49%of the maximum measured water level.The Parshall flume with a slope of 0.1%to 0.4%can better meet the accuracy of flow measurement,with the flow measurement accuracy being the highest at a slope of 0.1%.The Parshall flume has the best applicability under trapezoidal channels,with good sediment discharge capacity,and no sedimentation phenomenon on the flume body.