喷射器二维流场性能与结构的数值分析
|
摘要
喷射器是一种以不同的两股流体相互混合并发生能量交换以形成一股居中压力混合流体的装置,在众多工业领域有着广泛地运用,但是由于流体力学研究的困难以及喷射器内部极为复杂的流场,使得当前对喷射器的理论研究工作和喷射过程的探索还比较缺乏。长期以来喷射器的操作和设计都沿用一维理论,但是由于喷射器的三维结构和内部特殊的物理现象,这使得当前的一维方法不能为优化喷射器的工作条件和改进结构提供足够的理论依据。
本文借助大型流体分析软件FLUENT、用计算流体力学(CFD)的方法,实现了对蒸汽喷射器内部二维流场的数值模拟,详细探讨了喷射器的工作工程,特别对用CFD方法对实现喷射器数值模拟过程进行了全面的介绍与分析,对计算流体力学的基本思想、控制方程及其离散化、区域离散、湍流方程、离散方程的求解等CFD方法中的重要内容进行了阐述。对模拟结果深入分析,详细观察了喷射器内部的流动和特殊现象,透彻研究各因素尤其是工作蒸汽、引射蒸汽和出口蒸汽压力对内部流场、激波生成和喷射器性能的影响,并分析了原因。结果表明:提高工作流体压力并不总能提高喷射系数,一味提高其压力甚至还会引起工况的恶化,出口压力对喷射的性能有着重要的影响,喷射器只能在一定的背压下工作,超出背压后喷射器的性能急剧下降,喷射系数迅速降低。
除了工作参数对喷射器的性能有影响外,喷射器结构的优化同样对提高性能具有决定性的作用,已有的喷射器设计都是以在一维等熵假设基础上得到的半经验公式为指导的,这种方法可以预测喷射器的总体特性,但没有具体考虑喷射器各部分结构对喷射器性能产生的影响。为了解决这一问题,本文采用求解二维控制方程以模拟喷射器的内部流动,获得喷射器内部各参数的流场分布,同时充分利用数值模拟的灵活性、可重复性、低成本等优势,不断调整喷射器的各部分的结构形状、尺寸,对喷射器内部流场进行模拟计算并分析了结果,得出喷射器各部分结构对喷射器性能的影响规律。研究结果证明,改善喷射器的结构是提高喷射器效率的一个重要途径。
Ejector pump is a kind of equipment which makes mutual energy change of two kinds of fluids happen and commingles them into a mixed one. This machine is extensively used in various industries, however, the theory study and working-process research for the machine are slowly developed due to the complicated inside flow field of ejector and the deficient theory study of hydrodynamics. For a long time, the operation and design of ejector have followed the one-dimensional rule; nonetheless, the lagged one-dimensional rule could not provide enough theoretical support to optimize the operating condition and structural design since the configuration of ejector is three-dimensional and the physical phenomenon is special.
This dissertation adopts the fluid analytical software-FLUENT to realize the numerical analysis on the two-dimensional flow field and working-process of steam ejector through the method of CFD numerical simulation. It shows the realization process of this kind of numerical simulation comprehensively and especially; this article expounds the essence of CFD method: the elements, the governing equation, the discretization, the area discretization, onflow equation, the result finding process of discretization equation and so on. After the further analysis of simulation result, the careful observation of flowing phenomenon and special status inside ejector, and the investigation of possible contributing factors to the inside flow field, the generation of surging wave and the ejection performance especially like the pressure of operating-steam, jet-steam and mixed-steam, it comes to the conclusion that boosting pressure of operating-steam could not always enhance the performance, sometimes, if the pressure is exorbitant, it will deteriorate the flow field and make even worse operation. Conforming to the operating-steam, the mixed-steam pressure also has important influence to the performance. The ejector can only work normally under a given pressure number, and if the pressure of mixed-steam exceeds the number, the ejecting coefficient would come down quickly.
Except for working parameter, the configuration of ejector also plays a crucial part to capability. The existing design method is based on semi-empirical formula coming from one-dimensional constant entropy suppose. This formula can only forecast the overall performance, and it is helpless when comes to the idiographic part. In order to surpass this limitation, the paper, on one hand, displays the flow fields and parameter distribution by the method of result finding of two-dimensional flow fields; on the other hand, with the advantages of CFD (such as flexibility, repeatability and cost-saving), it shows the influence of configuration to ejector performance by adjusting the figuration and dimension of each part of ejector. The result of simulation proves that it is effective to enhance the working efficiency of ejector by optimizing the configuration of the machine.
本文借助大型流体分析软件FLUENT、用计算流体力学(CFD)的方法,实现了对蒸汽喷射器内部二维流场的数值模拟,详细探讨了喷射器的工作工程,特别对用CFD方法对实现喷射器数值模拟过程进行了全面的介绍与分析,对计算流体力学的基本思想、控制方程及其离散化、区域离散、湍流方程、离散方程的求解等CFD方法中的重要内容进行了阐述。对模拟结果深入分析,详细观察了喷射器内部的流动和特殊现象,透彻研究各因素尤其是工作蒸汽、引射蒸汽和出口蒸汽压力对内部流场、激波生成和喷射器性能的影响,并分析了原因。结果表明:提高工作流体压力并不总能提高喷射系数,一味提高其压力甚至还会引起工况的恶化,出口压力对喷射的性能有着重要的影响,喷射器只能在一定的背压下工作,超出背压后喷射器的性能急剧下降,喷射系数迅速降低。
除了工作参数对喷射器的性能有影响外,喷射器结构的优化同样对提高性能具有决定性的作用,已有的喷射器设计都是以在一维等熵假设基础上得到的半经验公式为指导的,这种方法可以预测喷射器的总体特性,但没有具体考虑喷射器各部分结构对喷射器性能产生的影响。为了解决这一问题,本文采用求解二维控制方程以模拟喷射器的内部流动,获得喷射器内部各参数的流场分布,同时充分利用数值模拟的灵活性、可重复性、低成本等优势,不断调整喷射器的各部分的结构形状、尺寸,对喷射器内部流场进行模拟计算并分析了结果,得出喷射器各部分结构对喷射器性能的影响规律。研究结果证明,改善喷射器的结构是提高喷射器效率的一个重要途径。
Ejector pump is a kind of equipment which makes mutual energy change of two kinds of fluids happen and commingles them into a mixed one. This machine is extensively used in various industries, however, the theory study and working-process research for the machine are slowly developed due to the complicated inside flow field of ejector and the deficient theory study of hydrodynamics. For a long time, the operation and design of ejector have followed the one-dimensional rule; nonetheless, the lagged one-dimensional rule could not provide enough theoretical support to optimize the operating condition and structural design since the configuration of ejector is three-dimensional and the physical phenomenon is special.
This dissertation adopts the fluid analytical software-FLUENT to realize the numerical analysis on the two-dimensional flow field and working-process of steam ejector through the method of CFD numerical simulation. It shows the realization process of this kind of numerical simulation comprehensively and especially; this article expounds the essence of CFD method: the elements, the governing equation, the discretization, the area discretization, onflow equation, the result finding process of discretization equation and so on. After the further analysis of simulation result, the careful observation of flowing phenomenon and special status inside ejector, and the investigation of possible contributing factors to the inside flow field, the generation of surging wave and the ejection performance especially like the pressure of operating-steam, jet-steam and mixed-steam, it comes to the conclusion that boosting pressure of operating-steam could not always enhance the performance, sometimes, if the pressure is exorbitant, it will deteriorate the flow field and make even worse operation. Conforming to the operating-steam, the mixed-steam pressure also has important influence to the performance. The ejector can only work normally under a given pressure number, and if the pressure of mixed-steam exceeds the number, the ejecting coefficient would come down quickly.
Except for working parameter, the configuration of ejector also plays a crucial part to capability. The existing design method is based on semi-empirical formula coming from one-dimensional constant entropy suppose. This formula can only forecast the overall performance, and it is helpless when comes to the idiographic part. In order to surpass this limitation, the paper, on one hand, displays the flow fields and parameter distribution by the method of result finding of two-dimensional flow fields; on the other hand, with the advantages of CFD (such as flexibility, repeatability and cost-saving), it shows the influence of configuration to ejector performance by adjusting the figuration and dimension of each part of ejector. The result of simulation proves that it is effective to enhance the working efficiency of ejector by optimizing the configuration of the machine.
引文
[1]索洛科夫,津格尔.喷射器[M].北京:科学出版社,1977.
[2] Abdalla M.Kishta.Designing, modeling, and testing solar water pump for developing countries [D]. Ames,Iowa: Iowa State University,2002.
[3] P. Havelka, V.Linek,J.Sinkule.Effect of the ejector configuration on the gas suction rate and gash old-up in ejector loop reactors [J].Chemical Engineering Science,1997,52(11):1701-1713.
[4] Peng Han, Xi Chen.Modeling of the supersonic argon plasma jet at low gas pressure environment [J].Thin Solid Films,2001,390 (8):181-185.
[5]尹述平,王国华.喷射技术在热电厂连排水回收中的应用[J].流体机械,2004,32(10):32-34.
[6] N. Deberne, J. F. Leone,A mode for calculation of steam in ejector performance, International Journal of Multiphase Flow,1999,25 (8) :41-85.
[7] Keenan J H, Neumannep. A simple air ejector [J]. Journal of applied mechanics, Trans ASME, 1942,64:75– 81.
[8] Keenan J H, Neumannep,Lustwerkf.An investigation of ejector design by analysis and experiment [J].Journal of applied mechanics,Trans ASME 1950,72:299– 309.
[9] Elrod H G.The theory of ejector [J].Journal of applied mechanics,Trans ASME,1945,67:170– 174.
[10] A.J.Yule,M. Damou,D. Kostopoulos.Modeling confine jet flow [J], Int.J.Heat and Fluid Flow, 1993,14(1):78-85.
[11] Lavrence Justin De Chant . Combined numerical/analytical perturbation solutions of the navier-stokes equations for aerodynamic ejector/mixer nozzle flows [D] . Texas A &M University,1997,5.
[12]阎尔平.蒸汽喷射式热泵供热在工业节能中的应用[J].节能,1994,1:33-36.
[13]王汝武.蒸汽加热系统节能及余热利用[J].食品与发酵工业,2004,30(9):148-150.
[14] A. Selvaraju, A.Mani.Analysis of an ejector with environment friendly refrigerants.Applied thermal Engineering,2004,24:827-838.
[15] Karl Willian Felson.Experimental investigation of an ejector scramjet RBCC at mach 4.0 and 6.5 simulated flight conditions [D].Huntsville:The University of Alabama,2002.
[16] H.Keenan,E.P.Neumann.A simple air ejector [J].Applied Mechanics,1942,64:75-81.
[17] J.H.Keenan, E.P.Neumann.An investigation of ejector design by analysis an experiment [J].Applied Mechanics,1950,72:299-309.
[18] B.J.Huang,J.M.Chang.A 1-D analysis of ejector performance [J].International Journal of Refrigeration,1999,22:354-364.
[19]李元章.蒸汽锅炉碱性排污水的综合利用[J].节能,2001,8:58-62.
[20]周雪漪.计算水力学[M].北京:清华大学出版社,1995.
[21]陶文铨.数值传热学[M].西安:西安交通大学出版社,2001.
[22]郭鸿志.传输过程数值模拟[M].北京:冶金工业出版社,1998.
[23]周光炯,严宗毅,许世雄等.流体力学[M].北京:高等教育出版社,2000.
[24]孔陇.工程流体力学[M].北京:高等教育出版社,2001.
[25] H.K. Versteeg,W.Malalasekera.An introduction to computational fluid dynamic: the finite volume [J].Wiley,1995,1: 35-39.
[26]黄克智,薛明德,陆明万.张量分析[M].北京:清华大学出版社,2003.
[27] Fluent Inc.Fluent user guide [Z].Fluent Inc,2003.
[28] J.O.Hinze.Turbulence [M].McGraw-Hill,New York, 1975.
[29] Fluent Inc.Fluent users defined function manual [Z].Fluent Inc,2003.
[30]易大义.数值分析引论[M].杭州:浙江大学出版社,1998.
[31]王副军.计算流体动力学分析——CFD软件原理与应用[M].北京:清华大学出版社,2004.
[32]李海军.喷射器性能、结构和特殊流动现象研究[D].大连:大连理工大学,2005.
[33]李海军,沈胜强,张博等.蒸汽喷射器流动参数与性能的数值分析[J].热科学与技术,2005,4(1):53-57.
[34]何培杰,吕俊贤,龙新平等.喷射泵内部流动数值分析[J].核动力工程,2005,26(2):135-139.
[35]张博,沈胜强,李海军等.二维流动模型的喷射器性能分析研究[J].热科学与技术,2006,2(2):149-153.
[36]杨燕勤,安志强,经树栋.进出口压力对喷射器性能影响的研究[J].矿山机械,2004, (32)12:11-13.
[37]徐海涛,桑芝富.蒸汽喷射式热泵变工况性能分析[J].热能动力工程,2003,18(4):395-398.
[38]沈维道,蒋智敏,童均耕.工程热力学[M].北京:高等教育出版社,2001.
[39]杨燕勤,安志强,经树栋.喉嘴距、面积比和引射压力对喷射器性能影响的研究[J].化工装备技术,2006,27(1):68-72.
[40]徐海涛,桑芝富.结构参数对蒸汽喷射压缩器性能的影响[J].南京工业大学学报,2003,25(3):28-33.
[41]张博,沈胜强,李海军.二维流动模型用于喷射器关键结构设计分析[J].大连理工大学学报,2004,44(3):387-391.
[2] Abdalla M.Kishta.Designing, modeling, and testing solar water pump for developing countries [D]. Ames,Iowa: Iowa State University,2002.
[3] P. Havelka, V.Linek,J.Sinkule.Effect of the ejector configuration on the gas suction rate and gash old-up in ejector loop reactors [J].Chemical Engineering Science,1997,52(11):1701-1713.
[4] Peng Han, Xi Chen.Modeling of the supersonic argon plasma jet at low gas pressure environment [J].Thin Solid Films,2001,390 (8):181-185.
[5]尹述平,王国华.喷射技术在热电厂连排水回收中的应用[J].流体机械,2004,32(10):32-34.
[6] N. Deberne, J. F. Leone,A mode for calculation of steam in ejector performance, International Journal of Multiphase Flow,1999,25 (8) :41-85.
[7] Keenan J H, Neumannep. A simple air ejector [J]. Journal of applied mechanics, Trans ASME, 1942,64:75– 81.
[8] Keenan J H, Neumannep,Lustwerkf.An investigation of ejector design by analysis and experiment [J].Journal of applied mechanics,Trans ASME 1950,72:299– 309.
[9] Elrod H G.The theory of ejector [J].Journal of applied mechanics,Trans ASME,1945,67:170– 174.
[10] A.J.Yule,M. Damou,D. Kostopoulos.Modeling confine jet flow [J], Int.J.Heat and Fluid Flow, 1993,14(1):78-85.
[11] Lavrence Justin De Chant . Combined numerical/analytical perturbation solutions of the navier-stokes equations for aerodynamic ejector/mixer nozzle flows [D] . Texas A &M University,1997,5.
[12]阎尔平.蒸汽喷射式热泵供热在工业节能中的应用[J].节能,1994,1:33-36.
[13]王汝武.蒸汽加热系统节能及余热利用[J].食品与发酵工业,2004,30(9):148-150.
[14] A. Selvaraju, A.Mani.Analysis of an ejector with environment friendly refrigerants.Applied thermal Engineering,2004,24:827-838.
[15] Karl Willian Felson.Experimental investigation of an ejector scramjet RBCC at mach 4.0 and 6.5 simulated flight conditions [D].Huntsville:The University of Alabama,2002.
[16] H.Keenan,E.P.Neumann.A simple air ejector [J].Applied Mechanics,1942,64:75-81.
[17] J.H.Keenan, E.P.Neumann.An investigation of ejector design by analysis an experiment [J].Applied Mechanics,1950,72:299-309.
[18] B.J.Huang,J.M.Chang.A 1-D analysis of ejector performance [J].International Journal of Refrigeration,1999,22:354-364.
[19]李元章.蒸汽锅炉碱性排污水的综合利用[J].节能,2001,8:58-62.
[20]周雪漪.计算水力学[M].北京:清华大学出版社,1995.
[21]陶文铨.数值传热学[M].西安:西安交通大学出版社,2001.
[22]郭鸿志.传输过程数值模拟[M].北京:冶金工业出版社,1998.
[23]周光炯,严宗毅,许世雄等.流体力学[M].北京:高等教育出版社,2000.
[24]孔陇.工程流体力学[M].北京:高等教育出版社,2001.
[25] H.K. Versteeg,W.Malalasekera.An introduction to computational fluid dynamic: the finite volume [J].Wiley,1995,1: 35-39.
[26]黄克智,薛明德,陆明万.张量分析[M].北京:清华大学出版社,2003.
[27] Fluent Inc.Fluent user guide [Z].Fluent Inc,2003.
[28] J.O.Hinze.Turbulence [M].McGraw-Hill,New York, 1975.
[29] Fluent Inc.Fluent users defined function manual [Z].Fluent Inc,2003.
[30]易大义.数值分析引论[M].杭州:浙江大学出版社,1998.
[31]王副军.计算流体动力学分析——CFD软件原理与应用[M].北京:清华大学出版社,2004.
[32]李海军.喷射器性能、结构和特殊流动现象研究[D].大连:大连理工大学,2005.
[33]李海军,沈胜强,张博等.蒸汽喷射器流动参数与性能的数值分析[J].热科学与技术,2005,4(1):53-57.
[34]何培杰,吕俊贤,龙新平等.喷射泵内部流动数值分析[J].核动力工程,2005,26(2):135-139.
[35]张博,沈胜强,李海军等.二维流动模型的喷射器性能分析研究[J].热科学与技术,2006,2(2):149-153.
[36]杨燕勤,安志强,经树栋.进出口压力对喷射器性能影响的研究[J].矿山机械,2004, (32)12:11-13.
[37]徐海涛,桑芝富.蒸汽喷射式热泵变工况性能分析[J].热能动力工程,2003,18(4):395-398.
[38]沈维道,蒋智敏,童均耕.工程热力学[M].北京:高等教育出版社,2001.
[39]杨燕勤,安志强,经树栋.喉嘴距、面积比和引射压力对喷射器性能影响的研究[J].化工装备技术,2006,27(1):68-72.
[40]徐海涛,桑芝富.结构参数对蒸汽喷射压缩器性能的影响[J].南京工业大学学报,2003,25(3):28-33.
[41]张博,沈胜强,李海军.二维流动模型用于喷射器关键结构设计分析[J].大连理工大学学报,2004,44(3):387-391.