Research On The Multi-Condition Optimization Of An Ultra High Specific Speed Axial Flow Pump

As one of the critical components in the inter-basin water diversion,flood drainage,as well as field irrigation,however,there is a technology gap in developing the domestic axial flow pump with high power in comparison with the relevant products in abroad.What's more,the excellent hydraulic models of axial flow pumps with various types are still limited;With the development of economics and technology,the demand of the high-specific-speed axial flow pump is increasing.Therefore,an ultra-high specific speed axial flow pump with its nominal value of 1500 was chosen to study in this work.In order to enlarge its high efficiency range and save energy,a multi-condition hydraulic optimization was proposed.The hydraulic design,parametric modeling and modern optimization method of axial flow pump were discussed based on the numerical simulation and computer technology.The main work and creative achievements are:1.The present research work both at home and abroad on the hydraulic design methods,internal flow of axial flow pumps as well as the relevant engineering optimization technology has been reviewed,including the difficulties in designing an ultra-high specific speed axial flow pump.2.The 3D model of the model axial flow pump was established and the internal flow under different operating conditions was numerically simulated by using the software ANSYS CFX.Meanwhile,a series of hydraulic performance tests of the model axial flow pump with various blade angles were carried out.The results show that:the specific speed of the axial flow pump is 1312,with its best efficiency point lower the design flow rate;the efficiency-flux curve shows a sudden drop at high flow rate;as the blade angle increases,the hydraulic performance curves show a shift towards high flow rate.What's more,the cavitation performances of the axial flow pump under different flow rates were also obtained from the test.As the flow rate increases,the critical value of NPSH decrease.The predicted hydraulic performances of the axial flow pump were in good agreement with the corresponding test data,even though,there is a high difference between them at lower flow rates.3.The streamline design method of axial flow pump is briefly introduced,7 critical geometric parameters of the axial flow pump were selected as the optimization variables and 18 kinds of test schemes were arranged based on the orthogonal test design method.The weighted average efficiency under 80%,100% and 120% of the design flow rate,respectively was set as the optimization object,through Fuzzy Analytic Hierarchy Process(FAHP),the optimized multi-condition hydraulic model of axial flow pump was established.Through range analysis,he best scheme is obtained,what's more,the hydraulic performances and the inner flow of every scheme were obtained based on numerical calculation and were compared in detail.The main conclusions are as follows:(1)The weighted average efficiency increases by 4.39%.Especially,the efficiency at large flow rate of 120% Qopt was obviously improved among other flow rates.The efficiency-flux curve shows that the best efficiency point of the pump moves to the large flow rate after optimization,and has a creeping drop at large flow rates,with a wider high-efficiency area in the curve.(2)The flow separation is prone to occur in the diffuser passages for axial flow pumps;the flow pattern after optimization was obviously improved with less vortex occurring at low flow rates and no flow separation formed at large and best efficiency flow rates.The hydraulic loss in the diffuser were significantly reduced.4.The software CFturbo and Pump Linx were first integrated on the Isight optimization platform by writing the script files and batch command,which realized the parametric design and intelligent multi-conditions optimization of axial flow pump.What's more,the Multi Island Genetic Algorithm was additionally applied to optimize the axial flow pump automatically based on this intelligent platform in this study.The main conclusions are:(1)Mesh generation in Pump Linx is easy to achieve,and the calculation accuracy is obviously higher than CFX at large flow rates with less time,which shows a great advantage in the optimization design of axial flow pump.(2)The flow rate and head of the axial flow pump at the design point were chosen as constraint conditions.The best efficiency point of the optimized axial flow pump with the increasing specific speed of 1471 was closer to the design flow rate,where the head reduces.What's more,the high-efficiency range was obviously broadened,which basically meet the design requirements.(3)The radial flow in the axial flow pump concentrated on the blade suction side,with the minimum radial velocity in the optimal condition;after optimization,the radial flow under different conditions have been improved,especially for the large flow rates,where the flow loss on blade surfaces were significantly reduced.(4)The velocity circulation in the impeller outlet and the axial velocity distribution were statistically analyzed,with their corresponding mathematical model established.(5)Finally,the optimized hydraulic model of the axial flow pump was manufactured and the hydraulic performance test under various blade angles were carried out.It can be found that:the maximum efficiency of the pump after optimization increased by 1.76% as the blade angle is 0 degree,and the corresponding head was slightly decreased,with the increased specific speed up to the value of 1450.What's more,the efficiency of the other angles have also been improved.