| In recent years,with the development of offshore platform oil development,large docks and other projects,the demands for vertical long-shaft fire pump have been increasing,which also put forward higher requirements of vertical long-shaft fire pump.Affected by tides,waves,typhoons and so on,the power of the vertical long-shaft fire pump increases dramatically with the increase of flow in the high submergence depth without cavitation excitation conditions,so there is a risk of motor power overload.Because of the complexity of the power system of this equipment,whose burn loss is huge,a larger safety factor supporting is usually used to solve this problem,which results in energy waste.The design of centrifugal pump with non-overload theory,can reduce the maximum of shaft power to help pumps working safely.Therefore,it’s important to study the pump characteristics without overload.At present,the domestic researches on the non-overload performance of pumps are mainly focused on low ratio velocity centrifugal pumps,and the researches on vertical long fire pumps are less,while the researches on their non-overload characteristics are still blank.Based on the theory of centrifugal pump without overload,this research has adopted CFD numerical simulation calculation,Particle Swarm Optimization algorithm(PSO),numerical simulation and test to optimize the design of vertical long-shaft fire pump,and then compared the energy characteristics,internal flow characteristics and pressure pulsation characteristics of the model before and after optimization.Then the energy characteristics,internal flow characteristics and pressure pulsation characteristics of the model before and after optimization have been compared and analyzed,and the impeller of the optimized model has been applied to the multi-stage vertical long-shaft fire pump.The contents of the research are as followed:(1)This paper has summarized the research status of vertical long-axis fire pumps and the research status of non-overload optimization design of centrifugal pumps at home and abroad.A reasonable application of PSO optimization algorithm method for optimizing pump geometry can improve the hydraulic performance of the pump to meet design requirements by summarizing the common pump design optimization method and degree of optimization of performance and analyzing the status of the application of PSO pump performance optimization.(2)The principle and structure of PSO algorithm have been introduced.Considering the characteristics of long pump performance numerical simulation cycle and low accuracy of optimization target,the standard particle swarm algorithm has been modified by using dynamically adjusted inertia weights and asynchronous learning factors of algorithm parameters.It seems that PSO algorithm is more suitable for pump design optimizations after testing five mathematical functions.(3)A vertical long-axis fire pump with a specific velocity of 137 has been selected as the research object,and the performance of this pump has been predicted by CFX17.0.The reliability of the simulation results has been verified by the energy characteristic experiments.The experimental values show good consistency with and numerical calculations values.In the design conditions,the shaft power error is 2.00%,the efficiency error is 5.93%,and the head error is 3.81%.In the fluid flow of 1.0Q_d,the fluid is separated from the second half of the impeller outlet,which has great effect on efficiency.When the flow increases to 1.5Q_d,the fluid separation phenomenon at the impeller outlet becomes more serious.Improving the inlet and outlet placement angle and wrap angle have been considered for subsequent optimization work to improve the flow.(4)Combining with the centrifugal pump non-overload theory,the non-overload optimization problem of the vertical long-axis fire pump has been analyzed to determine the six optimization parameters of the impeller and the optimization ranges of six optimization parameters.The KRIGING approximate model has been established on 28 sets of samples by the optimal Latin hypercube method,and the approximation model of the six impeller parameters has been optimized by the improved PSO algorithm.The best optimization scheme achieves overload characteristics within 1.5Q_d,while the 1.0Q_d efficiency value at rated operating point is increased by 1.63%,and the head is increased by 0.39m.(5)The internal flow characteristics of the optimized scheme have been analyzed,and the laws of parameters on the target have been obtained by analyzing the changes of energy characteristics and internal flow field before and after optimization.Non-constant calculations have been performed on the models before and after optimization to analyze the flow field changes of the impeller runner and the transition section between the impeller and guide vane in one rotation cycle for 1.0Q_d and 1.5Q_d operating conditions.The reasones for the non-overload characteristic within 1.5Q_d of the optimized scheme have been explored after analyzing the pressure pulsation phenomenons:the static pressure field distribution is relatively uniform in the rated operating conditions before and after optimization,while the optimized solution 1.5Q_d has a smaller pressure difference between the blades,which reduces the blade’s ability to do work and also verifies the theory that no overload characteristics can be achieved at the expense of large flow performance.;the optimized scheme obviously improves the pressure fluctuation in the pressure surface area of impeller in 1.0Q_d and 1.5Q_d condition,and reduces the amplitude of main frequency and secondary frequency.However,for the suction surface of impeller and the middle area between impeller and guide vane,only the pressure fluctuation of rated flow 1.0Q_d is improved.(6)The design concept of controlling the power characteristics in the first-stage impeller is proposed to provide a new design idea for the design of vertical long-shaft fire pumps without overload.The impellers of the original scheme and the optimized scheme have been combined to become a vertical long-shaft multistage pump,and the changes of energy characteristics and internal flow field of multiple combination schemes have been compared.The best combination scheme of two stages without overload is that the first stage impeller is the optimized scheme without overload impeller,and the secondary impeller is the high efficiency impeller of the original scheme.The best combination scheme of three stages without overload is that the first stage impeller is the optimized scheme without overload impeller,while the secondary and the final impellers are both the high efficiency impeller of the original scheme. |
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