Flow Pattern Analysis Of The Forebay And Startup Combination Optimization Of Dayudu Pumping Station

The forebay is the connecting section between the intake channel and the suction sump.In practical engineering,the bad flow pattern caused by the improper design of the forebay often occurs,especially the side inlet forebay is more prone to produce bias flow and backflow,which is difficult to meet the needs of safe operation of the pump station.Therefore,it is of great engineering value to improve the flow pattern in the side-inlet forebay by flow pattern adjusting measures.In this paper,taking the side-inlet forebay of Dayudu secondary pumping station as the research background,the flow pattern in the side-inlet forebay of pumping station and different pump startup combinations of pumping station was comprehensively studied by numerical calculation method,and the corresponding adjusting measures and pump startup combination suggestions were put forward,and the relationship between flow velocity and sediment volume fraction was explored.Firstly,the RNG k-ε turbulence model was used to simulate the single-phase flow pattern in the side-inlet forebay.The distribution and causes of the bad flow pattern were analyzed,and the adjusting schemes were proposed.During the operation of the pumping station,serious bias flow and backflow occurred in the forebay of the side inlet.The backflow area squeezed the main flow and made the main flow deflect to one side.Due to the water blocking effect of the breast wall,a large range of adverse flow patterns,such as vertical vortex,backflow and transverse flow,appeared in the suction sump.According to the flow characteristics in forebay,three kinds of adjusting schemes of diversion pier and combined adjusting scheme of arc diversion pier and adjusting grid are proposed.The results show that the diversion effect of arc-shaped diversion pier is better,which can effectively improve the bias flow phenomenon,reduce the distance between arc-shaped diversion pier and forebay inlet to achieve better water blocking and diversion effect,improve the average velocity uniformity,reduce the hydraulic loss,and further improve the flow pattern.The combination of arc diversion pier and rectifying grid can effectively eliminate the transverse flow at the bottom layer and make the velocity distribution at the bottom layer uniform,which provides a better inflow condition for the suction horn tube.After that,the flow pattern of forebay under different pump startup combinations was numerically simulated,and the variation law of flow pattern with different operation combinations was explored.According to the flow pattern,flow velocity uniformity and flow velocity distribution in forebay of pumping station under different operation combinations(six,three and two),different operation suggestions were given:if six units are worked,it is recommended to start six units from Unit G to Unit L near the end of the intake channel;If three units are worked,it is recommended to start three units from Unit J to Unit L near the end of the intake channel;The situation of starting two units is relatively special,so it is suggested to start two units Unit J and Unit K which are close to the end of the approach river and share the water suction sump.Finally,the mixture multiphase flow model was used to simulate the two-phase flow in the flow field to explore the relationship between velocity and sand volume fraction.According to the value of sand volume fraction obtained by two-phase flow calculation,the area where sand deposition may occur was judged,and the results were compared with the results of single-phase flow calculation.If the flow pattern in the low-speed area calculated by single-phase flow is relatively uniform,the low-speed area is basically consistent with the area with large sand volume ratio calculated by two-phase flow,while if there is bad flow pattern in the low-speed area,the low-speed area is not consistent with the area with large sand volume ratio.Therefore,when determining the possible location of sand deposition,we should not only rely on the flow velocity to judge,but also consider whether there are adverse flow patterns such as vortex and backflow in the low-speed zone.