Study On The Improvement Measures Of The Forebay In YuanQiao Pumping Station

The main function of forebay is to connect the water diversion channel and the inlet pool,which plays the role of smooth diffusion of water flow and uniform delivery of water flow to the inlet pool,providing satisfactory inlet condition for the pump.According to the direction of water flow,the forebay of a pumping station is divided into two forms:front inflow forebay and side-direction forebay.The curved section,vortex,deviation and other bad flow patterns will appear in the forebay if the front pool is improperly designed.This will directly affect the water intake performance of the pump,resulting in decreasing of the cavitation performance and operating efficiency of the pump,even cause noise and vibration of the pump unit,which may cause damage to the pipeline or components of the entire pump station system when the vibration is severe.Taking YuanQiao pumping station as an example,both numerical simulation and model test methods are adopted to select different measures to improve the flow patterns in the forebay.Rectifying analysis is conducted in the way of setting up diversion wall and column,and select the optimal scheme according to the actual project by analyzing the results of model test and numerical simulation.UG three-dimensional modeling software is selected for modeling.Firstly,3-D models of the original scheme is built and grid is meshed.Secondly,CFX is used to simulate the fluid flow in the forebay by giving a certain boundary condition.Then the results will be imported into Tecplot 360 for post-processing,and then the surface,middle and bottom flow diagrams will be exported.The velocity distribution uniformity and weighted average velocity angle of each inlet passage are calculated.In the study of the measures to improve the flow patterns of the forebay,numerical simulation on the diversion wall at different positions is carried out.By comparing the results of the distribution of flow field and the uniformity of velocity distribution,the following results are obtained:when the 1#direct diversion wall moves in the Y direction,the flow pattern of the 1#inlet passage becomes worse,while the flow pattern and the uniformity of the 2#inlet passage are gradually optimized.Then,the triangular columns and circular curved diversion walls are added to the scheme with the best rectifying effect of 2#passage.Aim to maintain a smooth flow in 2#inlet passage while improving the velocity distribution uniformity in 1#inlet passage,the combination of columns and diversion wall in different positions is simulated numerically,the optimal scheme of overall rectification is selected and the effect of rectification measures is discussed.In the end,the hydraulic model test of the original scheme and the rectification scheme is carried out,and the result is consistent with the numerical simulation,which verifies the rationality of the rectification scheme.Considering the calculation results of velocity distribution uniformity and weighted average velocity angle of each scheme,conclusions obtained are as following:the combined diversion wall and triangular column can effectively improve the flow patterns of the side-direction forebay so the water can flow evenly to the pump units,when the distance between 1#diversion wall and the sidewall is 4.77d,the triangular column is 3.45d from the sidewall,and the head of 1#arc guide wall is 4.77d from the sidewall,the head B of circular curved diversion walls is 6.23d away from the right wall,the rectification has the best effect.