第一章 CFD的基本原理-.ppt

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 code To u

2、nderstand sufficiently the underlying fluid dynamics to appreciate the scope and limitations of solutions To be able to assess the errors involved in CFD simulation To 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

3、理、机械工程、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:

4、The basics with applications. Mcgraw-Hill Companies, Inc. (1995) Uses finite difference approach Well 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

5、社 ，2009 Ferziger J H and peric M. Computational Methods for Fluid Dynamics. Springer 3ed 2001 excellent treatise on finite volume method for the mathematics and fluids expert,7,7,7,Important websites,Http://ejournal/JFE/. Journal of Fluids Engineering Http:/www.CFD- Http:/www.e- ht

6、tp:/www.qnet- Fluent user manual,8,8,8,8,Important Journals,Transactions of ASME Journal of Fluids Engineering Journal of Engineering for Gas Turbines Journal of Heat Transfer AIAA Journal Journal of Fluids Mechanics Proceeding of the IMechE,9,9,9,9,9,Available Commercial Codes,Fluent CFX FIDAP(基于有限

7、元方法和完全非结构化网格) PHOENICS AirPak STAR-CD FLOW3D NUMECA ,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,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,

8、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CFD CFD应用实例 CFD研究范围,85,CFD是英文Computational 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

9、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, F

10、IDAP, 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

11、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

12、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 by police), the oscillations took the form of a twisting motion that would cause the main section of the bridge to tilt at

13、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 Tacoma Narrows Bridge disaster illustrates two main points: 1) that fluid dynamics can play a role in many critical phenomena

14、 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 time and money.,The fundamental design flaw in the Tacoma bridge was a failure to account for the resonance vibrations g

15、enerated 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 such type of testing became standard for all future bridge designs.,93,The Tacoma Narrows Bridge disaster illustrate

16、s two main points: that fluid dynamics can play a role in many critical phenomena outside the traditional spheres of aerospace and mechanical engineering and that analysis of these phenomena 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,

17、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, Agra India 1631-1641,97,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-

18、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 Profiles,103,Single Dome Comparisons: Reynolds Number Variation,Reynolds Number = (U H/) = 1

19、85,000 Reynolds Number = (U H/ ) = 1,440,000 Conclusion: No significant difference,104,Double Dome ComparisonsApproach wind at 90o,105,Surface Pressures: Angles 0o, 45o & 90o,106,Pressure Coefficient Contours: Experimental vs 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C