Introduction to the Computer Exercices Turbulence: Theory and Modelling R.Z. Szasz, Energy Sciences, LTH Lund University

Transcription

1 Introduction to the Computer Exercices Turbulence: Theory and Modelling R.Z. Szasz, Energy Sciences, LTH Lund University

2 Outline VERY short CFD introduction Steps of problem solving The software used: OpenFOAM What is (not) OpenFOAM Basic use Introduction to Computer Exercise 1 Demo

3 Basic steps of CFD Problem Discretization Result Gov. Eq. BC Init. Cond. Solution OK?? u i u, t + ij, j +...

4 OpenFOAM basics This is just an introduction, NOT a manual, user guide, tutorial,... How to get it? Directory tree structure Solving a problem Pre-processing Running Post-Processing Further info

5 What is OpenFOAM? FOAM = Field Operation And Manipulation Mainly Computational Fluid Dynamics (CFD), but not only It is a toolbox (library) Open source C++ Example solvers, tutorials provided

6 How to get it Unix/Linux MS Windows In the followings the MS Windows version is shown, contact us if you intend to use it in Linux

7 Directory tree structure

8 Pre-processing: Grid Unstructured, finite volumes Tetrahedral, hexahedral, polyhedral, mixed In-built blockmesh Block-structured hexahedral mesh snappyhexmesh Unstructured hexahedral (from stl files) Import Gambit, Star-CD,...

9 OpenFOAM Designer (Windows only)

10 File -> New case

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12 blockmeshdict

13 blockmeshdict (2) Block-structured grid Scaling OF is SI Vertices Blocks Edges Boundary surfaces (Patches)

14 Mesh utilities Generation blockmesh View -> Refresh

15 Check these files fvsolution solution methods fvschemes discretization schemes controldict main control (timestep size, number of timesteps,...) polymesh grid transportproperties e.g. viscosity 0 initial conditions U velocity P - pressure

16 When everything looks OK: RUN (... and WAIT)

17 When ready:

18 Post-processing Paraview / ParaFOAM First create an empty file../casename/casename.openfoam

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20 Mark Region status Vol Field Status Apply

21 Display Scroll down Representation Surface Scroll up Color by U

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23 Increase timestep here

24 Paraview (cont.) Filter Post-processing routines File -> Save screenshot PNG, BMP, JPG, TIF,... Help Included in the installation

25 Further informations Documentation: User guide, Programmers manual

26 Computer Exercise 1 Flow around a circular cylinder for Re= Standard k-ε model Study influences caused by changing: model parameters Re

27 Standard k-ε + + = + j k T j j j x k x P x k u t k σ ν ν ε + + = + j T j j j x x k C P k C x u t ε σ ν ν ε ε ε ε ε ε ε ε ν µ 2 k T = C

28 Steps Download and uncompress ke_template.zip Copy ke_template to ke1. Start OpenFOAM Designer Open the ke1 case. Check the viscosity (constant/transportproperties) Check the turbulence model (constant/rasproperties) Check the initial/boundary conditions(0/*). Adjust if needed. Check the settings for the solver (system/controldict) Start the solver (Solvers/Incompressible/simpleFoam->Start) While running, discuss possible effects of changing model parameters.

29 Steps (contd.) Copy ke_template to ke2. Adjust C ε1 by at least 50% and start up the case. Start up similarly cases when C ε1 and C µ are modified. While running, start the post-processing program (Paraview, you can find the icon on the Task Bar) Load the plugins needed (Tools->Manage plugins, extensions), the two plugins are located in:...openfoam-1.5/bin/plugins/paraview/ Load case ke1, choose last timestep and mark all fields to load. Then click Apply.

30 Steps (contd.) Choose Surface instead of Outline Plot U, p, k, ε and analyze the results. Repeat the same for the cases with modified model parameters. Repeat the same for Re = 10 5 (using the standard set of parameters) Are the changes observed in the field variables as expected?