Study On The Improvement Measures Of The Flow Field In The Forebay Of A Hydropower Stationstation

The forebay is an intermediate structure between the diversion channel and the pressure pipe,and it is an important medium connecting them.It usually has the important function of redistributing the water flow and stabilizing the flow to reduce the impact of the water head and to suspend the suspended solids in the water.In the construction of early water diversion hydropower station,the design of the forebay is not reasonable because of the limited factors such as the geographical location of the hydropower station,the construction technology,the breadth of the foundation research of the forebay,and so on.At the same time,with the insufficient maintenance in the later period,many forebays in the water diversion station are often in the forebay.The disturbance of water flow in the pool,the obvious swirling vortex of the column and the drop of water surface,which make the unit unevenness unevenly,have a great influence on the safe operation of the hydropower station.Therefore,it is of great significance to take the necessary rectification measures to improve the flow pattern in the forebay for the improvement of the operation effect of the hydropower station,and can also provide some reference for other types of hydropower stations.In view of the uneven force of forebay,the author takes a hydropower station in Tianquan County of Ya’an as the research object.From the numerical simulation,the flow field in the front pool is studied with the model test,and a rectification measure to improve the unevenness of the unit output is put forward.The main contents and conclusions of this paper are as follows:(1)According to the actual survey results of the overall layout of the hydropower station and the operation of the generating units,the reasons for the uneven output of the units are theoretically analyzed.The theoretical analysis has preliminarily concluded that the unequal output of the four units of the power station is due to the unequal flow distribution of the unit,that is,the main factor that affects the output of the turbine is the flow of the machine,and the current capacity can be improved by the uniform flow.(2)The best turbulence model is determined by numerical simulation.The two turbulence models of RNG and Realizable are used to simulate the original forebay on the CFD software platform,and the numerical simulation results are compared with the actual operation situation of the forebay of the site,thus the optimal turbulence model is determined.The comparison results show that the RNG turbulence model is more suitable for the actual operation of the forebay of the hydropower station.(3)The RNG turbulence model is used to simulate the rectifying measures.The calculation results show that when the diversion wall is added in the forebay to rectify,the diversion wall has no obvious improvement on the uneven distribution of the flow in the forebay,and the rectifying measure of the bottom sill has an obvious effect on the uneven distribution of the flow in the forebay.Therefore,it is suggested that the bottom sill be used as a rectification measure for the forebay of the power plant.(4)The physical model test of forebay was carried out.The original forebay running under different water levels is simulated.Through the use of electromagnetic flowmeter and PIV test technology,the flow distribution of the pressure pipe in the forebay and the change of the flow field in the forebay are monitored.Through the comparison and analysis of the flow field and the outlet flow of the pipe in the numerical simulation and model test,the results show the numerical model.The flow field and outlet flow consistency of the proposed model are better than that of the model test,indicating that the numerical simulation of the front basin is reliable.The diversion wall and bottom cannon rectifying measures are added to the model to test the outlet flow and the flow pattern of the forebay under different operating water levels.The results show that the results obtained by the model test are basically consistent with the numerical simulation results,and the rectifying effect of the bottom ridge is better than that of the diversion wall,and the numerical simulation results have been effectively verified.