CFD的基本原理.ppt

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1、计算流体动力学Computational fluid mechanics,机械与动力工程学院凌祥,2,To provide the engineer with the understanding and practical experience required to use commercial CFD software for solving real engineering problems,Aim,3,Objectives,To learn how to solve problems in fluid dynamics using a commercial CFD codeTo und

2、erstand sufficiently the underlying fluid dynamics to appreciate the scope and limitations of solutionsTo be able to assess the errors involved in CFD simulationTo be able to interpret and present the results in an appropriate professional context,4,4,课程背景,Who should learn this course?动力工程及工程热物理、机械工

3、程、暖通、安全工程等专业研究生prerequisite courses for this course流体力学、Pro/E、高等数学、数值计算方法,5,5,教材,H K Versteeg and W Malalasekera.An Introduction to Computational Fluid Dynamics:the Finite Volume Method.Harlow,England:Pearson Eduaction Ltd.(1st Edition,2000)Anderson J D.Computational Fluid Dynamics:The basics with a

4、pplications.Mcgraw-Hill Companies,Inc.(1995)Uses finite difference approachWell written text excellent introduction,6,6,6,参考书,Patankar S V.Numerical Heat Transfer and Fluid Flow.NY:Mcgraw-Hill Companies,Inc.(1980)陶文銓.数值传热学.西安交通大学出版社(2004)陶文銓.传热与流动问题的多尺度数值模拟：方法与应用，科学出版社，2009Ferziger J H and peric M.C

5、omputational Methods for Fluid Dynamics.Springer 3ed 2001 excellent treatise on finite volume method for the mathematics and fluids expert,7,7,7,Important websites,Journal of Fluids Engineering流体中文网Fluent user manual,8,8,8,8,Important Journals,Transactions of ASMEJournal of Fluids EngineeringJournal

6、 of Engineering for Gas TurbinesJournal of Heat TransferAIAA JournalJournal of Fluids MechanicsProceeding of the IMechE,9,9,9,9,9,Available Commercial Codes,FluentCFXFIDAP(基于有限元方法和完全非结构化网格)PHOENICSAirPakSTAR-CDFLOW3DNUMECA,10,10,10,10,10,10,学习与授课,学自学动手大作业考核大作业期末考试（待定）,教学方式教师授课学生实践讨论学生Presentation,11

7、,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,第一章 计算流体动力学的基本原理,什么是CFD为什么要学习 CFD作为研究工具的CFD作为设计工具的CFDCFD应用实例CFD研究范围,85,CFD是英文Com

8、putational Fluid Dynamics（计算流体动力学）的简称。CFD是伴随着计算机技术、数值计算技术的发展而发展的。CFD相当于虚拟地在计算机做实验，用以模拟仿真实际的流体流动情况。,什么是CFD,86,CFD基本原理则是数值求解控制流体流动的微分方程，得出流体流动的流场在连续区域上的离散分布，从而近似模拟流体流动情况。可以认为CFD是现代模拟仿真技术的一种。1933年，英国人Thom首次用手摇计算机数值求解了二维粘性流体偏微分方程，CFD由此而生。1974年，丹麦的Nielsen首次将CFD用于暖通空调工程领域，对通风房间内的空气流动进行模拟。,什么是CFD？,87,CFD软件

9、是计算流体力学（Computational fluid Dynamics）软件的简称，是专门用来进行流场分析、流场计算、流场预测的软件。著名的CFD处理工具有以下一些：用于前处理：Gambit,Tgrid,GridPro,GridGen,ICEM CFD 用于计算分析：Fluend,FIDAP,POLYFLOW用于后处理：Ensight,IBM Open Visulization Explorer,Field View,AVS 提供综合的处理能力：Ansys，MAYA 特殊领域的应用：Icepak,Airpak,Mixsim,什么是CFD？,88,为什么要学习CFD,流体力学中有些问题采用实验

10、和理论的方法无法解决空天飞机,超声速燃烧冲压式喷气发动机高超声速（高马赫数-25，8000m/s）很高的气流温度没有风洞能模拟上述两方面,89,空天飞机是既能航空又能航天的新型飞行器。它像普通飞机一样起飞，以高超音速在大气层内飞行，加速进入地球轨道后，成为航天飞行器，返回大气层后，像飞机一样在机场着陆航天飞机返回再入大气层的空气动力学问题，曾经耗费了科学家们多年的心血，作了约10万小时的风洞试验。空天飞机的空气动力学问题比航天飞机复杂得多。因为飞机速度变化大，马赫数从0变化到25；飞行高度变化大，从地面到几百公里高的外层空间；返回再入大气层时下行时间长，航天飞机只有十几分钟，空天飞机则为l2小

11、时。,90,解决空气动力学问题的基本手段是风洞。目前，就连美国也不具备马赫数可以跨越这样大范围的试验风洞。即使有了风洞还需要作上百万小时的试验，那意味着就是昼夜不停地试验，也需要花费100多年的时间。只能求助于计算机，用CFD来解决，对那维尔斯托克斯方程进行求解,91,During the early morning hours,the Tacoma Narrows Bridge began to undulate violently in 35+mph winds.After several hours(and luckily after the bridge had been closed

12、 by police),the oscillations took the form of a twisting motion that would cause the main section of the bridge to tilt at up to a 45o angle from its original position.,On November 7,1940,one of the most spectacular engineering failures of the 20th century occurred in Tacoma,Washington.,92,The Tacom

13、a Narrows Bridge disaster illustrates two main points:1)that fluid dynamics can play a role in many critical phenomena outside the traditional spheres of aerospace and mechanical engineering and 2)that analysis of these phenomena during the design phase of a project can potentially save a lot of tim

14、e and money.,The fundamental design flaw in the Tacoma bridge was a failure to account for the resonance vibrations generated in the structure due to the aerodynamic forces.Subsequently,the replacement bridge design was tested a wind tunnel to measure potential wind effects before being built,and su

15、ch type of testing became standard for all future bridge designs.,93,The Tacoma Narrows Bridge disaster illustrates two main points:that fluid dynamics can play a role in many critical phenomena outside the traditional spheres of aerospace and mechanical engineering andthat analysis of these phenome

16、na during the design phase of a project can potentially save a lot of time and money.,94,为什么要学习CFD,95,为什么要学习CFD,流体力学的三种研究方法17世纪，实验流体力学（法国和英国)18和19世纪，理论流体力学（欧洲）20世纪70年代,96,作为研究工具的CFD,数值风洞（Numerical Wind Tunnel）风载荷圆屋顶（Smooth and Rough Domes）,Dome of the Rock Jerusalem,684 AD,Taj Mahal,AgraIndia 1631-1

17、641,97,作为研究工具的CFD,St.Peters Rome 1546-1564,北京国家大剧院,98,Velocity Contours:Umax=15 m/s,作为研究工具的CFD,Wind-Tunnel Initial Conditions,99,Grid Systems:One and Two Domes,100,Grid Systems:One and Two Domes,101,Hemisphere Grids,Boundary layer&Hex Grid,Boundary layer&Tet Grid,102,Single Dome Comparisons:Pressure

18、 Profiles,103,Single Dome Comparisons:Reynolds Number Variation,Reynolds Number=(U H/)=185,000Reynolds Number=(U H/)=1,440,000Conclusion:No significant difference,104,Double Dome ComparisonsApproach wind at 90o,105,Surface Pressures:Angles 0o,45o&90o,106,Pressure Coefficient Contours:Experimental vs

19、 Numerical:Approach wind at 0o,107,作为设计工具的CFD,108,作为设计工具的CFD,109,作为设计工具的CFD,110,作为设计工具的CFD,111,作为设计工具的CFD,112,CFD应用实例-Automobile,113,CFD应用实例-Aerospace,114,CFD应用实例-Chemical,Furnace Nox Reduction,115,CFD应用实例 Civil Engineering,Lower Monumental Dam Forebay,116,CFD应用实例-Multi-scale CFD applications,Eye 10

20、-5m,Turbine Blade 10-2m,Aircraft Engine 1m,Oil Reservoir 103m,Ocean Flow 105m,Binary Stars 1012m,117,计算方法高精度、高分辨率的计算方法并行算法遗传算法无网格算法,CFD研究范围,118,CFD研究范围,计算物理模型新的湍流模型多相流模型化学非平衡问题太阳风问题,119,CFD研究范围,网格技术网格与流动特征的相容性：对于某些复杂流动问题,如果使用传统的网格技术,无限加密网格,就可能使计算结果失真,此时就要求有构造与特征相适应的网格,例如在涡的周围镶嵌锥形网格。分块网格以及混合网格技术：分块网格主要用于处理复杂几何形式,也用于并行计算。混合网格技术包括矩形网格和非结构网格的混合使用。,120,应用领域拓展研究生物力学、生物医药航天航空，环境污染多相流动、微型机械流动电子技术高速火车高速船舶,CFD研究范围,