دادن خواص سيال

1. مدل k-εStandard k- Modelمزايا:بطور گسترده ای در صنعت مورد استفاده قرار مي گيرد.مقالات و اسناد بسيار زيادی پيرامون رفتار اين مدل منتشر شده است.اين مدل برای جريان توسعه يافته آشفته صادق است.برای بسياری از مسائل مهندسي ائم از جريان سيال و انتقال حرارت دقت قابل قبولي دارد.معايببرای هندسه هايي که انحنا زياد دارند، دقت اين روش پايين است.در مسائل بسيار پيچيده، افت فسار بسيار زياد نيز اين روش دقيق نيست.

2. دادن خواص سيال

3. شرائط کارکرد- تعريف فشار-تعريف شتاب جاذبهقابليت های فلوئنت

4. تعريف شرائط مرزي

5. شرط مرزي سرعت ورودی Velocity Inlets • تعريف بردار سرعت در ورود • براي وقتي که بردار سرعت ورودي معلوم مي باشد، قابل استفاده است. • برای پروفيل سرعت ورودی يکنواخت قابل استفاده است، در غير اينصورت بايد از UDF استفاده کرد. • در حالت جريان غير قابل تراکم باعث ايجاد شائط غير فيزيکي مي شود. • سعي کنيد که شرط مرزي سرعت در نزديکی مانع ورودی نباشد.

6. شرط مرزي سرعت ورودی

7. وارد کردن شرائط مرزي آشفتگي • چهار روش برای دادن شرط مرزي وجود دارد: • تعيين k و 

8. وارد کردن شرائط مرزي آشفتگي • چهار روش برای دادن شرط مرزي وجود دارد: • تعيين مقياس طولي آشفتگی و شدت آشفتگي Set turbulence intensity and turbulence length scale • خروجي از توربين Exhaust of a turbine Intensity (شدت آشفتگي)= 20 % Length scale(مفِاس طولي) = 1 - 10 % of blade span • جريان کملا توسعه يافته خروجي از يک کانال Fully-developed flow in a duct or pipe Intensity (شدت آشفتگي) = 5 % Length scale (مفِاس طولي) = hydraulic diameter

9. وارد کردن شرائط مرزي آشفتگي • چهار روش برای دادن شرط مرزي وجود دارد: • تعيين شدت آشفتگی و نسبت لزجت آشفتگی )Set turbulence intensity and turbulent viscosity ratio(

10. وارد کردن شرائط مرزي آشفتگي • چهار روش برای دادن شرط مرزي وجود دارد: • تعيين شدت آشفتگي و قطر هيدروليکی(Set turbulence intensity and hydraulic diameter)

11. incompressible flows compressible flows شرط مرزي ورودی- فشار • تعريف فشار کلي، دماي کلي، ساير پارامترهای اسکالر

12. شرط مرزي ورودی- فشار • تعريف جهت ورودی • عمد بر سطح • دکر جهت

13. شرط مرزي خروجي- فشار • تعريف مقدار فشار هيدروستاتيکي • در حالت جريان مافوق صوت، مقدار فشار هيدروستاتيکي در خروج از طريق برون يابي بدست مي آيد

14. شرط مرزي ورودی - دبي جرمي • تعريف مقدار دبي جرمي • در حالت جريان مافوق صوت، مقدار فشار هيدروستاتيکي در خروج از طريق برون يابي بدست مي آيد • جهت سيال ورودی • ساير پارامترهای مربوط به جريان آشفته

15. شرط مرزی ديوار(ديوار ساکن) - شرط عدم لغزش (No Slip)- تعيين تنش برشي سيال بر روی ديوار

16. شرط مرزی ديوار(ديوار متحرک) - انتقال - دوران-تعيين مولفه هاي سرعت

17. شرط مرزی حرارتي ديوار - شار گرمايي- دما-جابجايي

18. شرط مرزی حرارتي ديوار - شار گرمايي - دما-جابجايي

19. شرط مرزی حرارتي ديوار - شار گرمايي - دما-جابجايي

20. انتخاب جنس ديوار - پيش فرض فلوئنت برای ديوار آلومينيم مي باشد. برای فعال کردن بقيه خواص ديوار به شکل زير عمل مي کنيم:

21. Tri/Tet vs. Quad/Hex Meshes • For simple geometries, quad/hex meshes can provide high-quality solutions with fewer cells than a comparable tri/tet mesh. • For complex geometries, quad/hex meshes show no numerical advantage, and you can save meshing effort by using a tri/tet mesh.

22. Hybrid Mesh Example • Valve port grid • Specific regions can be meshed with different cell types. • Both efficiency and accuracy are enhanced relative to a hexahedral or tetrahedral mesh alone. • Tools for hybrid mesh generation are available in Gambit and TGrid. tet mesh hex mesh wedge mesh Hybrid mesh for an IC engine valve port

23. Non-Conformal Mesh Example • Nonconformal mesh: mesh in which grid nodes do not match up along an interface. • Useful for ‘parts-swapping’ for design study, etc. • Helpful for meshing complex geometries. • Example: • 3D Film Cooling Problem • Coolant is injected into a ductfrom a plenum • Plenum is meshed withtetrahedral cells. • Duct is meshed withhexahedral cells. Plenum part can be replaced with new geometry with reduced meshing effort.

24. Set Up the Numerical Model • For a given problem, you will need to: • Select appropriate physical models. • Turbulence, combustion, multiphase, etc. • Define material properties. • Fluid • Solid • Mixture • Prescribe operating conditions. • Prescribe boundary conditions at all boundary zones. • Provide an initial solution. • Set up solver controls. • Set up convergence monitors.

25. Compute the Solution • The discretized conservation equations are solved iteratively. • A number of iterations are usually required to reach a converged solution. • Convergence is reached when: • Changes in solution variables from one iteration to the next are negligible. • Residuals provide a mechanism to help monitor this trend. • Overall property conservation is achieved. • The accuracy of a converged solution is dependent upon: • Appropriateness and accuracy of the physical models. • Grid resolution and independence • Problem setup • A converged and grid-independent solution on a well-posed problem will provide useful engineering results!

26. Examine the Results • Examine the results to review solution and to extract useful engineering data. • Visualization can be used to answer such questions as: • What is the overall flow pattern? • Is there separation? • Where do shocks, shear layers, etc. form? • Are key flow features being resolved? • Are physical models and boundary conditions appropriate? • Are there local convergence problems? • Numerical reporting tools can be used to calculate quantitative results: • Lift and drag • Average heat transfer coefficients • Surface-averaged quantities

27. Tools to Examine the Results • Graphical tools • Grid, contour, and vector plots • Pathline and particle trajectory plots • XY plots • Animations • Numerical reporting tools • Flux balances • Surface and volume integrals and averages • Forces and moments

28. Consider Revisions to the Model • Are physical models appropriate? • Is flow turbulent? • Is flow unsteady? • Are there compressibility effects? • Are there 3D effects? • Are boundary conditions correct? • Is the computational domain large enough? • Are boundary conditions appropriate? • Are boundary values reasonable? • Is grid adequate? • Can grid be adapted to improve results? • Does solution change significantly with adaption, or is the solution grid independent? • Does boundary resolution need to be improved?

29. Review for Demo • Problem Identification and Pre-Processing 1. Define your modeling goals. 2. Identify the domain you will model. 3. Design and create the grid. • Solver Execution 4. Set up the numerical model. 5. Compute and monitor the solution. • Post-Processing 6. Examine the results. 7. Consider revisions to the model.

30. FLUENT DEMO • Startup Gambit • load database • define boundary zones • export mesh • Startup Fluent • GUI • Problem Setup • Solve • Post-Processing

31. Operating System Basics: Unix • Basic Unix commands: • pwd- prints the name current working directory • Your home directory is home/fluent/. • ls - lists the files in the current directory • cd- change working directories (cd ..to go up one directory). • The environment variable $TRAINPATH contains a shortcut to the directory where training files are stored. For example: cp $TRAINPATH/fluent5.x/tut/elbow/elbow.msh . will copy the mesh file for the first example problem into your current working directory. • To start Fluent 5: % fluent 2d & • To start Fluent 4.5: % fluent -r4.5 &

32. Operating System Basics: Windows NT • PC users will find tutorials under c:\Fluent.Inc\fluent5.x\ tut\. This directory is write-protected. • Save files to your home directory, c:\users\fluent\. • Fluent can be started from the command prompt or from the start menu: • Command Prompt • fluent 2d • Start Menu • Start Programs Fluent Inc Fluent 5.x • !Note: It is recommended that you restart Fluent for each tutorial for both Unix and NT systems to avoid mixing solver settings from different tutorials.