【作者】 孙强；

【导师】 刘明生； 伍悦滨；

【作者基本信息】 哈尔滨工业大学 ， 供热、供燃气、通风及空调工程， 2017， 博士

【摘要】 在热电厂或核电厂循环冷却水系统、城市供热和供水系统以及建筑内空调水系统等有压管道系统中,因阀门突然启闭或是水泵突然启停而导致管道中流速剧烈变化,常会引发水锤事故。传统水锤分析主要采用一维模型计算方法,该方法利用拟稳态摩阻模型近似计算管道瞬变流的摩阻耗散,因而无法准确模拟瞬变流的压力波衰减过程。准二维模型计算管道瞬时的二维速度场和一维压力场,并结合代数湍流模型计算瞬变流摩阻耗散,可以真实地反映瞬变流的压力波动,但现有求解方法因计算过程复杂仍无法在工程中广泛应用。因此,本文提出一维与准二维联合求解方法,该方法简化现有准二维模型计算方法的求解过程,同时可直接利用一维模型的分析策略,并与一维模型进行耦合求解,扩展准二维模型的应用范围并提高其计算效率。首先,分别阐述了一维特征线法和有限体积法,提出了改进的有限体积法,该方法的计算节点可以与特征线法的计算节点一一对应,同时验证了其准确性。基于理论分析,提出一维和准二维联合求解方法,分别建立了一维特征线法和改进的有限体积法与准二维模型联合求解的方法,并研究了这两种方法的准确性和高效性。结果表明,特征线法与准二维模型联合求解方法与现有准二维模型求解方法的计算精度相同,有限体积法与准二维模型联合求解方法的计算精度受粘性项权重系数的取值影响较大。在计算效率方面,本文所提出的计算方法比现有的准二维模型求解方法的计算效率更高,并且该方法可应用于一维交错网格。同时,提出修正的拟稳态摩阻模型。以文献中的实验数据为依据,比较分析了拟稳态摩阻模型、修正的拟稳态摩阻模型、改进的Brunone摩阻模型、Vardy-Brown摩阻模型和准二维模型的模拟结果。以准二维模型的模拟结果为依据,对修正的拟稳态摩阻模型中修正系数的选取规律进行了研究。其次,建立了基于准二维模型的离散蒸汽空穴模型和离散气体空穴模型,并以文献中的实验数据为依据,对比分析了拟稳态摩阻模型、改进的Brunone摩阻模型和准二维模型的离散蒸汽空穴模型和离散气体空穴模型的计算结果。结果表明,基于准二维模型的液柱分离模型相比一维模型的液柱分离模型的计算结果更准确,与文献中的实验结果更接近,可以准确地模拟气液两相瞬变流的压力波动过程。然后,基于事故停泵模型和压力罐模型,提出水泵-阀门-压力罐模型,并基于准二维模型的模拟结果,对传统一维模型模拟有压力罐防护的停泵水锤的准确性进行了研究。结果表明:准二维模型的压力波动的波峰和波谷值均小于一维模型的结果,并且准二维模型模拟得到的压力波动衰减速度更快。最后,基于上述准二维模型的模拟结果,利用序列二次规划法分别对三种不同连接结构的压力罐尺寸和参数进行了优化。结果表明,应用本文所绘制的最优罐体体积随管道允许最大压力和罐体连接结构参数的变化图,可简便直观地确定最优罐体体积和连接结构参数,并且在优化过程中应基于准二维模型的结果对一维模型进行修正,从而提高压力罐参数优化的准确性和适用性。本文提出一种基于一维模型与准二维模型联合求解瞬变流问题的计算方法,将该方法应用于校核一维摩阻模型、分析气液两相瞬变流流动过程、模拟事故停泵水锤及优化选择压力罐尺寸等方面,验证了该方法的准确性、高效性和适用性。本文的研究成果扩展了准二维模型的应用范围,进一步完善了瞬变流准二维模型的基本理论,对有压管道瞬变流分析具有指导意义,并为其用于实际工程的可行性提供了参考依据。更多还原

【Abstract】 The phenomenon of hydraulic transients could always happen,when valves open and close rapidly or pumps start and stop suddenly in recirculating cooling systems of thermal or nuclear power plants,civilian heating or water supplying systems,and air conditioning water systems in buildings.For these transient flow problems,one-dimensional(1D)numerical method is widely used to simulate the pressure surge.In the 1D method,a quasi-steady friction model is employed to calculate friction dissipation in transient pipe flows approximately.However,it could not accurately calculate the pressure wave attenuation process.Quasi-two-dimensional(quasi-2D)model could accurately simulate pressure fluctuations in transient flows.Because quasi-2D model calculates both two-dimensional(2D)velocity field and 1D pressure field,and it makes use of algebraic turbulence model to calculate friction dissipation in transient flows.Quasi-2D model,however,is not widely used in engineering applications due to the complicated calculation procedures of its existing solution methods.Therefore,we propose a new method,which combines 1D and quasi-2D models to solve the problems simultaneously.It is able to adopt the analysis strategy of 1D model directly and simplify the calculation procedures of the exsiting quasi-2D model solution methods.Moreover,it expands the range of applications and improves computational efficiency.Firstly,both method of characteristics(MOC)and finite volume method are presented.And an improved finite volume method is developed,in which calculation points are arranged with those in MOC correspondingly.The accuracy of the improved finite volume method is as well verified.Based on theoretical analysis,a combined solution method for both 1D and quasi-2D models is proposed.Moreover,both 1D MOC and improved finite volume method are employed to combine with quasi-2D model,respectively.The accuracy and efficiency of the two methods are studied.Results show that the method combining MOC with quasi-2D model has the same accuracy as the existing quasi-2D methods.The accuracy of method combining finite volume method with quasi-2D model is influenced by the value of weighting coefficient.The proposed method has much more efficiency than the existing quasi-2D methods,and it also could be used in 1D staggered grid.Meanwhile,a modified quasi-steady friction model is proposed.Based on experimental data in literature references,numerical results are compared and analyzed,which are calculated using quasi-steady friction model,modified quasi-steady friction model,improved Brunone friction model,Vardy-Brown friction model,and quasi-2D model,respectively.Based on numerical results of quasi-2D model,selection rules of correction factor in the proposed friction model are investigated.Secondly,both discrete vapor cavity model(DVCM)and discrete gas cavity model(DGCM)are combined with quasi-2D model separately are developed.Numerical results are compared with experimental data in literature references,which are acquired by the two models(DVCM and DGCM)combined with quasi-steady friction model,improved Brunone friction model,and quasi-2D model,respectively.Comparisons show that results of both DVCM and DGCM with quasi-2D model are more accurate than those calculated by DVCM and DGCM with 1D friction models,and DVCM and DGCM with quasi-2D model could accurately simulate pressure fluctuation in gas-liquid transient pipe flows.Then,a pump-valve-vessel model combining pump sudden stoppage model with air vessel model is proposed.According to the results of quasi-2D model,the accuracy of the traditional 1D model,which is used to simulate transient flow caused by pump sudden stoppage,is investigated.Results show that the pressure fluctuation simulated by quasi-2D model is smaller than that simulated by the 1D model,and the rate of pressure attenuation is faster.Finially,based on the results of quasi-2D model mentioned above,sequential quadratic programming is employed to optimize parameters of air vessel with three different connecting structures.Results show that optimal volume and connecting structure parameters could be directly confirmed,according to the plotted graph of both the optimal volume and the connecting structure parameters under different maximum allowable pressures.To improve the accuracy and applicability of optimization,the results of the traditional 1D model should be revised based on those of quasi-2D model.In this dissertation,the method combining 1D model with quasi-2D model to calculate transient flow is proposed.And it is used to verify the accuracy of 1D friction model,analyze transient flow in gas-liquid flow,simulate transient flow by pump sudden stoppage,and optimize air vessel parameters.The results in this dissertation expand the application range of quasi-2D model and refine the basic theory of quasi-2D model.It would be a great help to further understand mechanism of transient flow and provide guidance for practical projects.更多还原