空化对离心泵启动过程的影响分析

发布时间：2018-04-19 18:25

本文选题：离心泵 + 管路系统　；参考：《中国农业大学》2016年博士论文

【摘要】：离心泵在现代的生活生产以及消防安全中扮演者极其重要的角色,但是离心泵往往不是单独运行的,必然与管路、阀门等其他元件构成或大或小的工质传输系统。由于工质的可压缩性,系统在短时间内发生工况参数的剧烈变化时会形成水锤现象。当工质是水时,同时还会发生另一个复杂的现象——空化。如果在启动等过渡过程中出现空化,现象将更加复杂。本文将通过对有空化的离心泵的启动过渡过程进行分析来探讨空化对离心泵瞬变特性的影响。传统的特征线法(MOC)将所有的元件简化为一维模型进行计算,计算快速,但是无法获得有效的水力机械内部流动信息,同时还存在由于采用静态参数计算动态过程而引起的计算精度不足等问题。而针对水力机械的三维计算流体动力学分析(CFD)可以获得丰富的内流场信息,却不能兼顾系统特性；当考虑全系统三维计算尤其是考虑空化模型时,计算又将耗费大量资源。本文根据MOC和CFD基于流动方程的共性,引入基于MOC和CFD的含空化模型的耦合计算方法,在水力机械和管阀系统的交界面实现流量和压力信息的交换,从而利用有限计算资源完成管阀系统与水力机械考虑空化的过渡过程同步计算。论文的主要工作如下：1、根据已有的泵启动试验结果,对试验台进行了一维建模,对离心泵进行水力设计与性能优化以满足对比分析需求。分析了一维模型计算结果与试验结果的差别；分析了水泵空化特性与试验用泵的空化性能的匹配情况。管路一维模型及水泵三维模型都能满足后续对比分析的要求。2、搭建MOC与CFD耦合计算平台。通过三维数值模拟软件Fluent以及一维特征线计算软件Flowmaster所提供的接口,建立起瞬态计算过程中流量信息和扬程信息交换的路径。分析了耦合计算中权重因子、耦合时步内迭代次数等参数对收敛速度及精度的影响。3、对离心泵的0.5s无空化启动工况进行了耦合计算。通过与试验结果和纯一维计算结果对比,耦合计算结果准确合理,验证了耦合算法用于离心泵启动过渡过程分析的可行性。分析了启动过程中互相影响的水泵内流场和管路节点的物理特性变化。在此基础上也对1s启动工况进行了预测计算,分析了启动时长对系统稳定性的影响。4、对离心泵的0.5s有空化启动工况进行了耦合计算。分析了耦合计算结果与传统DVCM空化模型计算结果以及试验结果的差别,分析了两种计算方法的优缺点。通过耦合计算,对试验中启动过程水泵出口压力出现两次降低现象的原因进行了详细讨论,计算结果表明,两次出口压力降低的原因是水泵进入初生空化区导致的扬程下降效应强于转速升高导致的扬程升高,导致了第一次压力降低,进入空化工况区则导致了第二次压力降低。5、分析了水泵在不同的空化启动工况下流场内部的压力脉动特性、叶轮力特性、空泡发展演变规律,发现了与传统稳态空化非定常分析中呈现出的不同的空化场压力波动现象以及空泡形态变化特点,并通过对比分析揭示了二者不同的原因。为分析水泵启动过程中管路和水力机械相互影响下的流动特性和空化发展过程,本文建立并验证了离心泵及其管路系统启动过渡过程考虑空化模型的MOC-CFD耦合计算方法,并用此方法对水泵系统启动过程进行了分析,并对几个特殊的物理现象及其机理进行了探讨。本文的研究内容和结论对于研究受空化影响的水力机械及系统瞬变特性具有指导意义。
[Abstract]:Centrifugal pumps play an important role in modern life production and fire safety, but centrifugal pumps are often not operated separately, and must be composed of other components, such as pipes and valves, or large or small transmission systems. Due to the compressibility of the working quality, the system will be formed in a short period of time. Water hammer phenomenon. When the working fluid is water, there will also be another complicated phenomenon, cavitation. If cavitation occurs during the transition process, the phenomenon will be more complicated. This paper will discuss the effect of cavitation on the transient characteristics of centrifugal pump by analyzing the starting transition process of the centrifugal pump with cavitation. The traditional characteristic line method (M OC) all the components are simplified as one dimensional model, and the calculation is fast, but the effective internal flow information of the hydraulic machinery can not be obtained. At the same time, there are still some problems due to the insufficient calculation precision caused by the dynamic process using static parameters. And the three-dimensional computational fluid dynamics analysis (CFD) for hydraulic machinery can be obtained. The rich internal flow field information can not take into account the system characteristics. When considering the whole system three-dimensional calculation, especially the cavitation model, the calculation will consume a lot of resources. Based on the commonness of MOC and CFD based on the flow equation, the coupling calculation method based on the MOC and CFD based cavitation model is introduced, and the interface between the hydraulic machinery and the pipe valve system is introduced. In order to realize the exchange of flow and pressure information, the finite calculation resources can be used to complete the synchronous calculation of the transition process of the tube valve system and the hydraulic machinery considering the cavitation. The main work of this paper is as follows: 1, based on the existing test results of the pump starting, one dimensional modeling is carried out on the test bed, and the hydraulic design and performance optimization of the centrifugal pump are satisfied to meet the requirements. The difference between the calculation results of one dimension model and the test result is analyzed. The matching between the cavitation characteristic of the pump and the cavitation performance of the test pump is analyzed. The one-dimensional model of the pipeline and the three dimensional model of the pump can meet the requirement of the follow-up comparison analysis.2, and the coupling calculation platform of the MOC and the CFD is set up. The three-dimensional numerical simulation software Fl is built. Uent and the interface provided by the one dimensional feature line computing software Flowmaster, establish the path of flow information and the exchange of head information during the transient calculation, and analyze the influence of the weight factors in the coupling calculation and the number of iteration times on the convergence speed and the precision of the coupling,.3, which has been carried out for the 0.5s non cavitation starting condition of the centrifugal pump. The coupling calculation is compared with the experimental results and the results of the one dimension calculation. The coupling calculation results are accurate and reasonable. The feasibility of the coupling algorithm used in the analysis of the start-up transition process of the centrifugal pump is verified. The internal flow field of the pump and the physical characteristics of the pipe node in the start-up process are analyzed. On this basis, the starting condition of the 1s is also introduced. The influence of the start time on the stability of the system.4 was analyzed. The coupling calculation of the 0.5s cavitation starting condition of the centrifugal pump was carried out. The difference between the results of the coupling calculation and the results of the traditional DVCM cavitation model and the test results were analyzed. The advantages and disadvantages of the two methods were analyzed. The coupling calculation was used to start the test. The cause of the two reduction in the outlet pressure of the pump is discussed in detail. The calculation results show that the decrease of the two outlet pressure is due to the rise of the head drop effect caused by the water pump entering the primary cavitation area, which is stronger than the rise of the lift caused by the rise of the speed, leading to the reduction of the first pressure and the entry into the cavitation condition zone. The pressure fluctuation characteristics in the flow field inside the water pump, the characteristics of the impeller force and the evolution law of the cavitation are analyzed by the two pressure reduction of.5. The variation of the cavitation field pressure fluctuation and the change of the cavitation form are found out in the non steady analysis of the traditional steady cavitation, and it is revealed by comparison and analysis. In order to analyze the two different reasons. In order to analyze the flow characteristics and the process of cavitation development under the mutual influence of the pipeline and the hydraulic machinery during the pump starting process, the MOC-CFD coupling calculation method of the cavitation model in the start-up transition process of the centrifugal pump and its pipeline system is established and verified, and the starting process of the pump system is divided by this method. A few special physical phenomena and their mechanism are discussed. The contents and conclusions of this paper are of guiding significance for the study of the transient characteristics of hydraulic machinery and system affected by cavitation.

【学位授予单位】：中国农业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TH311

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