本文選題：離心泵 + 管路系統(tǒng)��； 參考：《中國農業(yè)大學》2016年博士論文

【摘要】：離心泵在現(xiàn)代的生活生產(chǎn)以及消防安全中扮演者極其重要的角色,但是離心泵往往不是單獨運行的,必然與管路、閥門等其他元件構成或大或小的工質傳輸系統(tǒng)。由于工質的可壓縮性,系統(tǒng)在短時間內發(fā)生工況參數(shù)的劇烈變化時會形成水錘現(xiàn)象。當工質是水時,同時還會發(fā)生另一個復雜的現(xiàn)象——空化。如果在啟動等過渡過程中出現(xiàn)空化,現(xiàn)象將更加復雜。本文將通過對有空化的離心泵的啟動過渡過程進行分析來探討空化對離心泵瞬變特性的影響。傳統(tǒng)的特征線法(MOC)將所有的元件簡化為一維模型進行計算,計算快速,但是無法獲得有效的水力機械內部流動信息,同時還存在由于采用靜態(tài)參數(shù)計算動態(tài)過程而引起的計算精度不足等問題。而針對水力機械的三維計算流體動力學分析(CFD)可以獲得豐富的內流場信息,卻不能兼顧系統(tǒng)特性；當考慮全系統(tǒng)三維計算尤其是考慮空化模型時,計算又將耗費大量資源。本文根據(jù)MOC和CFD基于流動方程的共性,引入基于MOC和CFD的含空化模型的耦合計算方法,在水力機械和管閥系統(tǒng)的交界面實現(xiàn)流量和壓力信息的交換,從而利用有限計算資源完成管閥系統(tǒng)與水力機械考慮空化的過渡過程同步計算。論文的主要工作如下：1、根據(jù)已有的泵啟動試驗結果,對試驗臺進行了一維建模,對離心泵進行水力設計與性能優(yōu)化以滿足對比分析需求。分析了一維模型計算結果與試驗結果的差別；分析了水泵空化特性與試驗用泵的空化性能的匹配情況。管路一維模型及水泵三維模型都能滿足后續(xù)對比分析的要求。2、搭建MOC與CFD耦合計算平臺。通過三維數(shù)值模擬軟件Fluent以及一維特征線計算軟件Flowmaster所提供的接口,建立起瞬態(tài)計算過程中流量信息和揚程信息交換的路徑。分析了耦合計算中權重因子、耦合時步內迭代次數(shù)等參數(shù)對收斂速度及精度的影響。3、對離心泵的0.5s無空化啟動工況進行了耦合計算。通過與試驗結果和純一維計算結果對比,耦合計算結果準確合理,驗證了耦合算法用于離心泵啟動過渡過程分析的可行性。分析了啟動過程中互相影響的水泵內流場和管路節(jié)點的物理特性變化。在此基礎上也對1s啟動工況進行了預測計算,分析了啟動時長對系統(tǒng)穩(wěn)定性的影響。4、對離心泵的0.5s有空化啟動工況進行了耦合計算。分析了耦合計算結果與傳統(tǒng)DVCM空化模型計算結果以及試驗結果的差別,分析了兩種計算方法的優(yōu)缺點。通過耦合計算,對試驗中啟動過程水泵出口壓力出現(xiàn)兩次降低現(xiàn)象的原因進行了詳細討論,計算結果表明,兩次出口壓力降低的原因是水泵進入初生空化區(qū)導致的揚程下降效應強于轉速升高導致的揚程升高,導致了第一次壓力降低,進入空化工況區(qū)則導致了第二次壓力降低。5、分析了水泵在不同的空化啟動工況下流場內部的壓力脈動特性、葉輪力特性、空泡發(fā)展演變規(guī)律,發(fā)現(xiàn)了與傳統(tǒng)穩(wěn)態(tài)空化非定常分析中呈現(xiàn)出的不同的空化場壓力波動現(xiàn)象以及空泡形態(tài)變化特點,并通過對比分析揭示了二者不同的原因。為分析水泵啟動過程中管路和水力機械相互影響下的流動特性和空化發(fā)展過程,本文建立并驗證了離心泵及其管路系統(tǒng)啟動過渡過程考慮空化模型的MOC-CFD耦合計算方法,并用此方法對水泵系統(tǒng)啟動過程進行了分析,并對幾個特殊的物理現(xiàn)象及其機理進行了探討。本文的研究內容和結論對于研究受空化影響的水力機械及系統(tǒng)瞬變特性具有指導意義。
[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.

【學位授予單位】：中國農業(yè)大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TH311

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