| Small and medium-sized pumping stations typically use pump sumps as the inlet structure of the pumping station.The design of the structural dimensions and flow field uniformity of the pump sump are important parameters that affect the safe and stable operation of the pumping station.Poorly designed pump sump structural parameters can cause adverse flow patterns such as large-scale backflow and vortices in the pool,which can develop and propagate inside the pump,leading to increased noise and vibration of the pump unit and even affecting the start-up operation of the unit.This study focuses on the Songchao Pump Station project in the Huaihe River estuary waterway,and uses computational fluid dynamics(CFD)to simulate the pump unit by changing the two main design parameters of the inlet pool’s bottom floor clearance and backwall clearance.The study emphasizes the analysis of the impact of different design parameter schemes on the hydraulic performance of the pump unit and the internal flow field of the inlet pool.By studying the changing morphology of unsteady vortex structures and the characteristics of pressure pulsation,this research further reveals the impact of design parameter changes on the uniformity of the internal flow field of the omega-shaped enclosed inlet pool.The research findings of this study contribute to the reduction of vortex and turbulence in the inlet pool,ensuring the safe and stable operation of the pump station unit,and provide important guidance for practical engineering construction and inlet pool design.This paper investigates the effects of changes in the main design parameters of a ω-shaped closed pump sump on the hydraulic performance and internal flow field of a pump device.The results show that when the bottom floor clearance C is set to 0.3D,the performance curve significantly decreases,with a maximum difference in head of 0.12m and 2%reduction in efficiency.Additionally,the high-speed area at the front of the bellmouth inlet is closer to the low-speed area near the back wall distance,which accounts for almost 2/3 of the bellmouth inlet area.The velocity distribution is uneven,and the uniformity of the outlet cross-sectional flow velocity and the weighted average angle are reduced by 7.1%and 1.8°,respectively.Changes in the backwall clearance have a relatively small impact on the overall performance of the pump device,with a maximum difference in head and efficiency of 0.016m and 0.6%respectively.The maximum difference in flow velocity uniformity and weighted average angle due to changes in the back wall distance is 0.85%and 1.1°,respectively.In terms of the internal flow field,with decreasing suspension height,a clear bottom vortex appears at the bellmouth inlet,and the bottom of the inlet structure is subjected to greater dissipation due to the influence of vortices.As the backwall clearance increases,the area of the boundary vortex gradually increases,with relatively minor changes in entropy production.The influence of different design parameters on the pressure pulsation characteristics in the pump device is explored.As the bottom floor clearance decreases,the pulsation amplitude at the same monitoring point inside the pump device significantly increases,especially at the diffuser and impeller inlets.However,changes in the backwall clearance have little effect on the pulsation amplitude at different flow rates,indicating that changes in the bottom floor clearance have a greater impact on pressure pulsation.Based on the vortex distribution results in the pump sump during changes in the bottom floor clearance,it was found that the vortex core position changes with the bottom floor clearance,and the impact of vortices generated at different bottom floor clearances on pressure pulsation within the pump device varies.The bottom of the inlet pool is greatly affected by bottom vortex disturbance.At a bottom floor clearance of C=0.3D,the monitoring point at the location of the bottom vortex has a maximum pulsation amplitude in design and high-flow conditions that is approximately 3.57 times and 4.28 times greater than that of the monitoring point not affected by vortices,respectively.The pulsation amplitude at the same monitoring point increases with flow rate,and at high-flow conditions,it is about 1.44 times greater than that of the design conditions,indicating that the vortex disturbance at the bottom of the pump sump is more significant at high-flow conditions.According to the vortex zone at the bottom of the pump sump,the influence of the scheme with or without the guide cone on the hydraulic characteristics of the pump device is analyzed.The study shows that the use of a guide cone improves the efficiency of the pump device by 0.64%,as well as the velocity uniformity and weighted average angle at the outlet of the pump sump,compared to the no guide cone scenario.Under different working conditions,the guide cone effectively eliminates the bottom vortex in the pump sump,preventing the development of vortex conditions and enabling water to flow more evenly into the impeller region.The high-entropy region generated at the bottom of the inlet tank is significantly reduced,and the pressure pulsation at the impeller inlet is also improved.Under the design working condition,the pressure pulsation amplitude at monitoring points in the impeller inlet,from the impeller rim to the hub,is reduced by 8%,5%,and 4%,respectively,with the use of a guide cone. |
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