Study On Inflow Hydraulic Characteristics Of Fenghuangjing New Pumping Station Under Water Diversion Condition

Fenghuangjing is an old pumping station with a two-way flow channel,due to the limitation of the civil structure of the inlet and outlet channels,the width of the inlet and outlet channels is small,resulting in extremely uneven distribution of water velocity under the horn tube of the inlet channel,along with the water flow disorders,blockages and so on,negatively affecting the operation safety of the pump.As a water intake building,the forebay plays the role of smoothly leading the aqueduct to the inlet pool and improper design and operation will cause problems such as siltation at the bottom of the pool,large-scale backflow and whirlpool in the pool.Therefore,in order to ensure the stability,safety and efficiency of the pumping station,it is necessary to ensure a uniform spread of water flow in the forebay.The new pumping house of Fenghuangjing was built in the forebay of the old pumping station which aims to increase the volume of water from the Yangtze River to the Huaihe River and cooperate with the irrigation water supply.This project took the segment of the old pumping station and the forebay of new pumping station as an example,conducting the combination of model test and numerical simulation to study the hydraulic characteristics of the flow pattern in the old pumping station and the forebay.The research contents are as follows:In order to solve the problems existing in the flow pattern of the new pumping station under the original design,the software NX11.0 was adopted to construct the calculation model of Fenghuangjing Pumping station and the MESH pre-processing was carried out to divide the grid and generate the grid needed for calculation.Finally,the Fluent software was adopted to simulate the flow pattern of the old pumping station and the forebay of the New Pumping Station.The calculation results show that there was a dead water area between the old pumping station and the forebay and the water flow was constantly tumbling.At the same time,there was a large backflow vortex at the units on both sides of the forebay which extends from the water surface to the bottom and spreads to the inlet pool,affecting the normal inflow operation of the side unit.In order to improve the bad flow pattern in the circulation channel of the old pumping station,different optimization measures were proposed for the layout of the old pumping station on the basis of the original design scheme.After the outflow segment of the old pumping station was changed to streamline,the flow pattern at the junction of the old pumping station and the forebay was obviously improved.However,due to structural reasons,the flow velocity difference between the upper and lower layers was large and the non-synchronization of the upper and lower inflow still existed.After retaining the channel of pumping house in the old pumping station,the confluence problem of the upper and lower layers of the old pumping station was improved and the uniformity of flow velocity was obviously improved.Aiming at the problem of poor water flow conditions in the forebay,the rectification optimization was carried out by adding eight-shaped diversion piers of different lengths and columns of different arrangement forms.After comparative analysis,it can be concluded that the effect of rectification by using columns was the best.By arranging columns,the water flow in the forebay can be redistributed and the area of the raceway in the forebay can be effectively reduced,so that the flow can enter the New Pumping Station more evenly and smoothly.Accordingly,the arrangement of the column has a great influence on the rectification effect and for this project,the multi-combined column rectification effect was the best,to be specific the area of the raceway in the forebay was reduced and the flow velocity uniformity of the 1#～6#channel section was improved.Based on numerical simulation,combined with the hydraulic model test,the flow pattern and velocity distribution under the typical scheme were compared and analyzed,so as to test the rationality and calculation accuracy of the numerical simulation optimization scheme.The research on the layout structure and forebay of the old pumping station carried out in this paper can provide improvement schemes and opinions for the design and construction of Fenghuangjing New Pumping Station,ensuring the safe and stable operation of Fenghuangjing New Pumping Station and providing reference and technical support for similar projects in nature reserves.