| Object: Accurate water measurement is an important guarantee for the rational allocation of irrigation water,and irrigation area water measurement technology restricts the modernization and development of irrigation areas.Therefore,in order to improve the excellent water measurement,high-efficiency water use,and agricultural water saving in irrigation areas,and to accelerate the construction of an environment-friendly society,it is of vital significance to improve the accuracy of channel measurement.Methods: Based on previous studies,this paper takes Parshall grooves as the research object,and establishes different types of inlet connection sections(internal arc transition section,circumscribe arc transition section,straight transition section,and no transition section)through modeling software.Using the CFD software to mesh three-dimensional structure model and numerical simulation calculation,analyze the changes of water surface line,water head loss,flow measurement accuracy,flow velocity and pressure of 4 kinds of inlet connection section under different working conditions,and propose a The connection section with the highest water delivery efficiency provides a theoretical basis for the practical application of the Parshall flume.The main research contents and conclusions are as follows:Results:(1)Establish a numerical model of the hydrodynamics of the Parshall flume.The RNG k-ε turbulence model can handle curved streamlines and swirling conditions well,and the structured grid is suitable for dividing regular geometric bodies.Comprehensive analysis of numerical simulation and hydraulic test data shows that the average error between the two is 2.25%.The numerical simulation research method shows its advantages of strong adaptability,wide application,and short test period,providing effective means for actual engineering research.(2)The hydraulic characteristics of the flow in the Parshall flume are analyzed.The fluctuation of the water surface line is affected by the boundary conditions.In the case of free flow,the water surface line transitions smoothly from upstream to downstream;in the case of submerged flow,the water surface line fluctuates more than the free flow,and the height of the downstream water surface varies with the degree of submergence The increase of the increase.Streamlines are sparsely distributed in the upstream contraction section and densely distributed in the downstream divergent section.The boundary contour of the velocity cloud graph is consistent with the boundary contour of the water surface line.In the case of free flow,the flow velocity of the water flow increases sequentially along the direction of the flow of water,and the velocity distribution is uniform.The submergence of the flow causes the throat section of the Parshall flume to overflow.The pressure cloud diagram shows the same law under the conditions of free flow and submerged flow.The hydrostatic pressure increases with the increase of water depth.During the installation and construction of the Parshall flume,the lining should be reinforced at the upstream connection section to prevent Excessive hydrostatic pressure results in the deformation of the Parshall flume structure,resulting in flow measurement errors.(3)The flow measurement accuracy of different schemes is studied.Through many experiments and analysis,it is found that there is a significant exponential fitting relationship between the water level and the flow rate,and the flow measurement accuracy is highest when the upstream connection section is a straight connection section.(4)The local head loss value of the Parshall flume under various working conditions is analyzed.In the case of free flow,the maximum value of the local head loss is 0.22 and the minimum value is 0.09;in the case of submerged flow,the maximum value of the local head loss is 0.165 and the minimum value is 0.05.In the case of free outflow,the value of local head loss is greater than that of submerged flow,and the value of local head loss decreases as the degree of submergence increases.(5)A preliminary investigation on the flow pattern of the Parshall flume has been done,and the results show that the flow patterns of the free flow and the submerged flow are consistent.In the range from the inlet of the Parshall flume to 1.4m is subcritical slow;in Pakistan The water flow is a critical flow in the range from 1.4m to 1.6m of the inlet of the Parshall flume;the water flow is a supercritical flow in the range of 1.6m from the inlet of the Parshall flume to the downstream outlet of the Parshall flume.Conclusion: The hydrodynamic model of Parshall flume is constructed based on computational fluid dynamics,revealing its internal three-dimensional flow field hydraulic characteristics;verifying that the error between hydraulic test data and numerical simulation is 2.25%;exploring the water surface line,velocity cloud graph,pressure cloud graph,and Buddha Rude’s number distribution law;revised flow calculation formula,proposed an optimized structure model with higher flow measurement accuracy,and the direct transitional flow measurement accuracy was the highest. |
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