Analysis And Improvement For Flow Pattern In Pumping Station Hub Forebay Based On Three-dimensional Numerical Simulation

The forebay is an important component part of the pumping station,and its funciton is to make the stream spread evenly and smoothly when the stream flows from the approach channel to the inlet conduit,so that it can supply a better flow pattern for the pumping station.However,in the engineering practice,when the pumping station and the sluice are arranged side by side,the flow pattern in the forebay is very complicated and can not meet the requirements of engineering operation.Therefore,it is significant for the efficient and stable operation of each building to improve the flow pattern in the forebay through certain measures.A pumping station hub is a parallel arrangement of pumping station and sluice,it consists of three pumping units and two-hole sluice.Based on the engineering construction of the pumping station hub and the sofeware of FLUENT,the numerical simulation of the flow pattern in the forebay is carried out by using the Reynolds Navier-Stokes equations and the standard turbulence model.The flow pattern in the forebay is quantitatively evaluated according to the proposed improvement objective,and the effective improvement measures are proposed for the flow pattern problems in the forebay.The main study resluts are as follows:(1)When the pumping station hub operates,some undesirable flow patterns such as vortices and strong lateral flow appeared in the forebay of the original scheme.In order to improve the flow pattern in the forebay and the flow condition for the pump,three improvement measures are studied.Firstly,a pier is used to connect the pier of the cleaning machine bridge with the middle piers between the adjoining pump units and the middle pier in the inlet conduit.The problem of transverse flow in the original scheme is effectively solved,and the vortex in the forebay is restrained and the northward deviation of the main stream is reduced.Secondly,the influence of the diversion pier length on the flow pattern in the forebay is carried on,the results show that the longer the diversion pier length,the water flow can be adequately adjusted before flowing into the inlet conduit,the more conducive to the improve the forebay flow pattern.Thirdly,the influence of the bottom slope on the flow pattern in the forebay is carried on,the results show that along with bottom slope slowing down,the vortex intensity and the scope in the bottom of forebay is gradually reduced or even disappeared,the inlet section velocity distribution uniformity has been enhanced,the flow pattern in the forebay has been obviously improved.(2)When the drainage sluice is running,at the north hole entrance of the original scheme of the sluice gate there is a large vortex,which will squeeze the main stream,make the flow velocity distribute unevenly,increase the hydraulic loss and reduce the flow capacity of the sluice.The guide wall added in the front of the drainage sluice entrance and between the two holes plays a good diversion function.The vortex scope on the back water side of the north hole entrance is reduced,the squeezing phenomenon of the inlet flow is obviously reduced,and the flow distribution in the south and north holes is greatly improved.The arc-shaped guide wall is better than broken-line guide wall for improving the inlet flow pattern of the drainage sluice.(3)In order to fully understand the flow pattern in the forebay under different start-up combinations of pumping station,the flow patterns in the forebay are studied under seven kinds of start-up combinations.The results show that the flow in the forebay is smooth,the flow velocity is uniform,and there is no harmful vortex in the forebay,it provides good hydraulic conditions for the flow flowing into the inlet conduit smoothly.