Multi-objective Optimization And Cavitation Characteristics Of Volute Mixed-flow Pump Based On ISIGHT Platform

Volute type mixed flow pump is widely used in farmland irrigation and drainage and industrial water engineering because of its high efficiency,reliability,wide application range and convenient maintenance.In response to the call for national energy conservation and emission reduction policies,the field of multi-objective optimization of volute mixed-flow pumps has a very broad prospect.The research object of this paper is a volute type mixed-flow pump with a specific speed of 433.To improve the hydraulic efficiency and head of the design working condition,the ISIGHT platform combined with the NSGA-? optimization algorithm is used to design the impeller and volute of the mixed-flow pump.The parameters were optimized by multi-objectives,and the cavitation performance of the volute type mixed flow pump before and after optimization was compared and analyzed.The main contents and results of this paper are as follows:(1)Three-dimensional modeling of the volute and impeller of the volute type mixed flow pump was carried out by using UG software,and steady computation under multiple operation conditions of the mixed-flow pump was simulated by ANSYS software.The simulation results of the internal flow field show that there is a large area of low pressure area at the inlet of the impeller,and there are obvious vortex and reflux phenomena near the tongue,which reduces the hydraulic performance of the mixed-flow pump.(2)Integrating UG,ICEM CFD and ANSYS CFX software in ISIGHT optimization platform,an automatic optimization system is established for parametric modeling,mesh division and flow field numerical calculation comparison.The design parameters of the mixed-flow pump are selected as the optimization variables to improve the hydraulic efficiency and lift in the design conditions,and the anti-cavitation performance and the match characteristics between the impeller and the volute are set as constraints,and the multi-objective optimization of the model pump design parameters is carried out.And through the CFD technology to compare the hydraulic performance under the design conditions before and after optimization,verify the feasibility and effectiveness of the optimization method.(3)The numerical simulation results before and after the comparison show that the hydraulic efficiency of the mixed-flow pump is about 2.85% higher than that of the prototype pump,the lift is increased by 2.864%,and the high efficiency zone of the mixed-flow pump is widened.After optimization,the static pressure distribution in the pump is more uniform and reasonable,and the vortex and backflow in the vicinity of the tongue are improved,so that the fluid flow at the tongue is smoother and the energy loss is reduced.The fluid in the section VIII is smaller than that in the pre-optimized pulsation diffusion region,which improves the local increase of the turbulent kinetic energy.(4)Combined with the theory of cavitation dynamics and computational fluid dynamics,the numerical simulation of gas-liquid two-phase flow constant flow is carried out on the volute mixed-flow pump to analyze the cavitation characteristics of the mixed-flow pump before and after optimization under various working conditions.The focus is on the volume fraction of cavitation and the distribution of cavitation in the pump before and after optimization under different available NPSH values.The results show that the initial cavitation occurs at the inlet of the blade suction side close to the front shroud before and after optimization.As the pressure inside the pump decreases,the bubble gradually diffuses into the middle of the impeller.When the available NPSH is low enough,the whole flow path will be blocked by cavitation bubbles.The comparison of cavitation performance in multiple operation conditions shows that the proper reduction of the flow quantity is beneficial to the suppression of cavitation,and the cavitation performance of the large flow quantities declines rapidly.After optimization the cavitation areas and large-volume fractional cavitation reduce significantly on the same inlet pressure under various operation conditions,indicating that the multi-objective optimization improves the cavitation characteristics of the mixed-flow pump and meets the optimized design requirements.