| The forebay is an important part of the pumping station project.Its main function is to make the flow diffuse smoothly during the operation of the pumping station.The design of the forebay of the pumping station should meet the requirements of uniform flow velocity,smooth flow and no vortex in the pool.According to the inflow direction,the forebay of pumping station can be divided into two basic types:positive inflow and lateral inflow,there is a direct relationship between flow pattern and diffusion angle in forward inflow forebay.According to the specification requirements,the reasonable value range of the diffusion angle of the front pool is between 20°and 40°.Excessive diffusion angle is more likely to produce bad flow patterns.The flow pattern in the intake pool is affected,which will affect the flow pattern in the inlet pool,worsen the water inlet condition of the pump unit,reduce the operation efficiency of the pump,and even affect the normal operation of the pump station.Therefore,it is of great significance to take certain rectification measures to improve the flow pattern in the forebay of large diffusion angle pumping station for improving the operation efficiency,safe and economic operation and management of such pumping stations.The research object of the paper is a positive inlet pump station with a diffusion angle of 55° in the forebay.The research method of numerical simulation and hydraulic model test is adopted.In view of the adverse flow pattern in the forebay,the wedge diversion pier is set in the forebay to conduct rectification analysis.The main contents of this paper are as follows:(1)UG modeling software is used to establish the three-dimensional model of the diversion river and the influent structure.The numerical simulation software CFX is used to calculate the original scheme,and the results are imported into Tecplot 360 for data post-processing,so as to draw the flow state of the surface layer and bottom layer of the forebay and intake tank.The flow velocity uniformity and weighted average angle are used as quantitative evaluation indexes to analyze the causes of adverse flow patterns in the original scheme and the influence on the flow pattern in the intake pool,and the rectification measures are put forward.(2)The wedge diversion pier is set at the inlet of the forebay,12 rectification schemes are designed and numerical simulation is carried out.And the evaluation indexes of flow field distribution,cross-section velocity uniformity and velocity weighted average angle under each rectification scheme are comprehensively compared.The following conclusions are obtained:The wedge diversion pier can play a diversion role well at the inlet of the forebay,and the flow can enter the 1#and 4#inlets smoothly,but the unreasonable position and geometric factors will have a greater adverse effect on the influent conditions of the 2#and 3#inlets.When the top angle of the wedge diversion pier is too small,the diversion effect on the flow is weakened,and the influence on the flow pattern of the forebay is small.When the top angle is large,but the bottom length is small,the influence on the flow pattern of the forebay is small.Then,the optimal rectification scheme is explored by using multiple wedge diversion piers.The combined symmetrical wedge diversion pier at the inlet of the front pool has better rectification effect.On the basis of not affecting the inlet conditions of 2 and 3 inlet tanks,the water flow pattern in 1 and 4 inlet tanks was effectively improved.(3)According to the relevant engineering data,the hydraulic test model was established at the scale of 1:15,and the model tests of the original scheme and 8 rectification schemes were carried out.The flow field distribution in the forebay and the flow velocity distribution uniformity in the cross section of each scheme were integrated.The results of the model test were consistent with those of the numerical simulation,which verifies the rationality of the rectification scheme. |
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