Flow Characteristics And Combined-Sill Adjusting Flow In Forebay Of Multi-Unit Pumping Station

The forebay of a pumping station is a hydraulic structure connecting the intake canal and the pump intake sump,the forebay is divided into forward and lateral intake forebays.The flow pattern of the forebay directly affects the flow pattern of the intake sump and the operation of the unit,disturbance of flow pattern will lead to large-scale backflow in intake sump,reduced efficiency of pumping units,sediment deposition may occur in severe cases,vibration and cavitation phenomena of pump units,affecting unit operation safety.So,the flow pattern in the forebay is very important,in order to optimize the flow state of forebay,achieving results by adding different adjusting flow measures,provide a good water intake environment for the operation of pumps,ensuring the safety,reliability and efficiency of pump unit operation,avoid vibration and refluxThis paper takes a pumping station as engineering background,how to rectify flow characteristics of forebay of multi-unit pumping station.The research methods are divided into two parts:numerical simulation and model experiment.The numerical simulation results show that there is a large-scale backflow in the forward intake forebay of multi-unit pumping stations,and it seriously affects the velocity distribution of cross section in front of the intake sump.Under different operating conditions,large area of reflux still exists in forebay,even the main flow deviates.Data processing of model measurement,the large area backflow on both sides of the forebay is basically consistent with the numerical simulation.The uniformity of velocity in the middle layer of the forebay outlet section calculated by numerical simulation is 25%,the uniformity of velocity in the middle layer measured by experiments is 21%,which is basically match.The position and size of the reflux in the forebay are in good agreement with those calculated by numerical simulation when different units are opened.It can be concluded that the numerical simulation results given in this paper are credible.Adjusting flow of forward intake forebay for multi-unit pumping stations,the measure adopted is to add a bottom sill in the forebay,with the addition of a bottom sill,set up a distance of 2.24Hw from the intake sump,the height of the bottom sill is 0.4Hw and a distance from intake sump is 4.48Hw.,the scheme of 0.5Hw bottom sill height,the experimental and numerical simulation results show that the adjusting flow of a bucket cannot simultaneously meet the requirements of eliminating the backflow in the forebay and uniformity of cross-section velocity at the outlet of the forebay.Two bottoms are used for adjusting flow,through different bottom sill heights,different distances and two bottom sills at different positions are analyzed and studied.Comparisons of flow characteristics and cross-section velocity uniformity in forebay under different schemes,the recommended parameter scheme of two sill are selected as follows:The height of the first bottom sill is 0.5Hw,the height of the second bottom sill is 0.4Hw,the relative distance between the two bottom sill is 2.24Hw,the distance between the second bottom sill and the intake sump is 2.9Hw,and the width of the bottom sill is 0.3Hw.Two bottom sills with recommended parameters optimize the large area reflux in the forebay to basically no reflux,the uniformity of laminar velocity at the outlet section of forebay has been greatly improved,the upper layer increased from 31.2%to 45%,middle level increased from 25%to 66%,meet the requirements,It can make the flow velocity uniformity and flow pattern in the intake sump more conform to the specifications.1#Unit Closing and 1#6#Unit Closing,Large area symmetrical reflux exists in forebay,and 1#unit shutdown will lead to mainstream bias.After adding the recommended two sills schemes,the large area reflux and deviation in the forebay are effectively solved.