Orthogonal Optimization Design Study Of Pump As Turbine Based On Vane Load Distribution

We are currently in a phase of social development known as the "carbon neutrality" and "peak carbon" era.Actively strengthening the development of high-quality energy requires two main approaches.Firstly,it involves increasing the development and utilization of renewable energy sources.Secondly,it entails optimizing the allocation of resources and improving energy efficiency.Pump As Turbine(PAT)technology,due to its simple internal composition,short development cycle,and convenient maintenance,has been widely applied in small-scale hydropower development and the recovery of industrial waste energy.This technology is well suited to meet the current demands of economic energy development,environmental protection,and low-carbon economy.However,when a pump is directly used as a turbine,certain issues may arise,such as secondary flow,flow separation,and reduced efficiency due to the fact that the design of centrifugal pumps does not consider the operating conditions of turbines.These issues can lead to inefficiency and flow instability.Furthermore,in the forward design process,the selection principle for blade profiles is as follows: the planar streamline should be smooth and continuous,ensuring unidirectional bending without any S-shapes.Each blade profile should exhibit symmetry,although there is no specific standard for this.In this study,a centrifugal pump with a specific speed of 69 was chosen as the research object.The focus was on investigating the effects of the load curve and the blade’s high-pressure edge inclination angle on the Pump As Turbine(PAT)performance.By analyzing the data,the load distribution pattern suitable for PAT was determined.Based on this,modifications were made to the blade’s load distribution and high-pressure edge inclination angle for a single-stage single-suction centrifugal pump with a specific speed of 86.A numerical simulation was conducted,and a comparison was made with the original pump to demonstrate the feasibility of this pattern.Main research contents of this paper:(1)The research object selected in this study is a low-specific-speed centrifugal pump(specific speed of 69)used as a Pump As Turbine(PAT).Through numerical simulations,hydraulic performance analysis and research were conducted on both the pump operating conditions and the turbine operating conditions using orthogonal experiments.Four main factors affecting blade load and the high-pressure edge inclination angle of the blades,totaling five factors,were selected.Based on these factors,16 sets of impellers were designed at different levels.By calculating the results of the orthogonal experimental design,range analysis was performed to determine the primary and secondary order of influence of each factor level on the pump operating conditions(head and efficiency)and the turbine operating conditions(efficiency).Additionally,the individual factor influence patterns were determined.This analysis ultimately led to the optimal design solution for the Pump As Turbine.(2)Based on Computational Fluid Dynamics(CFD)numerical simulation,the optimal impeller design obtained from the orthogonal experiments and the original design were subjected to steady-state simulations.The results of the orthogonal experiments revealed that the impeller with the optimal load distribution,compared to the original impeller,still met the design requirements for the pump operating conditions,with a 1.6% increase in hydraulic efficiency.For the turbine operating conditions,the hydraulic efficiency at the design point increased by 3.5%,and the optimal high-efficiency point improved by 4%.In addition,unsteady-state simulations were conducted for the turbine operating conditions,revealing improvements in pressure fluctuations at the interface between the stationary and rotating components,as well as at the tongue and diffuser regions.Analyzing the results of the orthogonal experiments,the load distribution pattern suitable for pump-as-turbine blades was summarized.As pump-as-turbine systems typically use medium-to-low specific-speed pumps in reverse as turbines,a centrifugal pump with a specific speed of 86 was selected to validate the derived load distribution pattern.Compared to the original impeller,the optimized impeller exhibited a 0.12% increase in hydraulic efficiency for pump operating conditions.For the turbine operating conditions,the hydraulic efficiency at the design point increased by 1.24%,and the optimal high-efficiency point improved by 1.76%.Additionally,the amplitude of pressure fluctuations decreased in both cases.(3)By comparing the load distribution,external characteristic curves,internal flow fields,and pressure fluctuations in the turbine operating conditions between the original and optimal designs of the two pumps,it was observed that when the load distribution pattern was such that the front cover plate experienced forces in the middle-front position and the rear cover plate experienced forces in the rearward position,it resulted in an improvement in both the efficiency of the centrifugal pump operating conditions and the efficiency of the turbine operating conditions.Additionally,the flow state at the impeller inlet and the efficiency characteristics in the turbine operating conditions showed some improvement when selecting the high-pressure edge inclination angle of the blades,thus alleviating the occurrence of pressure fluctuations.