OpenFOAM/C3/Creating-and-Meshing-aerofoil-in-Gmsh/English

Tutorial: Creating and Meshing an aerofoil in Gmsh

Script : Gautam Sharma

Narration : Rahul Joshi

Keywords: Meshing, aerofoil, Gmsh, OpenFOAM.

Visual Cue	Narration
Slide 1	Hello and welcome to the spoken tutorial on Creating and Meshing an aerofoil in Gmsh
Slide 2 : Learning Objectives	In this tutorial we will learn to How to create an aerofoil using Gmsh Mesh the created aerofoil
Slide 3: Pre-requisite	To practice this tutorial, the user should have basic knowledge of aerofoil and Gmsh. If not, for Gmsh please see the tutorial on Installing and running Gmsh on the spoken tutorial website.
Slide 4: System Requirement	To record this tutorial, I am using Ubuntu Linux Operating system version 14.04 and Gmsh version 2.8.3
Slide 5: About aerofoil	Let me introduce you to aerofoil. Aerofoils are streamline shaped wings which are used in airplanes and turbo machinery. These shapes are such that the drag force is a very small fraction of the lift.
Show the aerofoil	This is a picture of an aerofoil.
Slide 5 : The dat file Download the dat file and Python script	The predefined coordinates for aerofoil are available in simple text file with .dat extension. I will download the .dat file and Python script from this url: http://community.dur.ac.uk/g.l.ingram/download.php
Open in browser http://community.dur.ac.uk/g.l.ingram/download.php Open the Downloads folder	Let me open the website. Download the .dat file and the Python script and go to the Downloads folder.
Copy-paste files	Copy and paste these files from the Downloads folder to Desktop.
Open naca5012xyz.dat file	Open the .dat file. This file contains the calculated X and Y coordinates for each point that defines the aerofoil. Z coordinate is kept as zero. We need the X, Y and Z coordintes in Gmsh acceptable format. This can be done manually but this is time consuming.
Open Python script	Now open the Python script. This Python script converts the data in the .dat file and gives the ouput in a separate file which is understood by Gmsh.
Open the terminal	Now open the Terminal window. Type cd space Desktop
Run the python Script python dat2gmsh.py naca5012xyz.dat	Now type python space dat2gmsh.py space the name of the dat file and press Enter. Now type ls. We can see that a new file by the name naca5012xyz.dat .geo will be generated.
Open naca5012xyz.dat.geo	Open the geo file. This contains the co-ordinates in Gmsh format. Here nac_lc is the characterstic length which is defined in the first line which is 0.005 I will change this to 0.5 This is because we need a coarser mesh. You can change this value according to your mesh requirement. Now save this file.
Open file in gmsh	In the terminal window, type gmsh space name of the geo file and press Enter. This opens gmsh with the aerofoil.
Zoom in at the tail	Now zoom in, by scrolling at the tail end of the aerofoil. You will note that the aerofoil has an open trailing edge.
Close gmsh	Close gmsh.
Open the .geo file with text editor again	Now go back to the .geo file. Scroll down.
Add the point	We will add the last point and join it. Now above spline, enter Point(1046) = { 1.005, -0.0005, 0.00000, nac_lc};
Modify the spline >> save the file	Modify the spline as Spline(1000) = {1000:1046,1000}; Save the geo file.
Open .geo file in gmsh	Open the modified file in Gmsh. We can see that the edge is joint.
Set up a boundary around the aerofoil	Now we will make a boundary around the aerofoil using points. Enter these coordinates and change the prescribed mesh element size to 0.5 Press Enter.
Enter the points as (4 3 0) (4 -3 0) (-4 -3 0) (-4 3 0)	Similarly, add the other points. (4 3 0) (4 -3 0) (-4 -3 0) (-4 3 0)
Join the points by Straight lines	Now join the points with a straight line.
Define the surface	Now click on Plane surface and select the surface boundary.
Select the aerofoil	Zoom in and select the aerofoil as the hole boundary.
Press e to end selection	Press e to end selection. You can see we have our surface.
Extrude the surface Translate>extrude surface	Now we will extrude the surface to make it 3D. Go to Translate >> Extrude Surface.
	A new window will appear asking for cordinates for translation.
Enter the coordinates for Z direction Click on boundary surface	Since we want to extrude the surface in positive Z direction, enter the coordinates for Z direction as 1 and click on the boundary of the surface.
Press e to end selection	Press e to end selection.
Click to move the geometry	Use the left click of the mouse to move the geometry. You can see that the geometry has been extruded.
Close	Close this. Close the gmsh window
Open the geo file	Open the geo file.
Go to Extrude	Scroll down and go to Extrude.
Add these lines inside extrude	Inside Extrude add these lines : Layers{1}; Recombine; Save this file. This will ensure that the mesh is one element thick.
Open the geo file in terminal	Now in the terminal window, open the geo file.
Generate the mesh	Now we have our geometry, we will do the meshing. Gmsh automaticaly generates the mesh of the defined geometry.
Go to Mesh >> click on 1D mesh >> 2D mesh >> 3D mesh	Go to Mesh. Click on 1D mesh, 2D mesh and 3D mesh. The mesh has been generated.
	You may notice that the mesh is finer near the aerofoil and gets coarser as we move towards the boundary.
Refine the mesh	We can also refine the mesh by clicking on the Refine by Splitting parameter in the mesh menu.
Save your work	Now let us save our work.
Click on Save as >> Ok >> Ok	Go to File menu and click on Save as. A new window will appear. In the drop down, change to the mesh format. And type the name the file as aerofoil.msh Note that here msh stands for the file type mesh. Click Ok Again click Ok
Slide : Assignment	This brings us to the end of the tutorial. As an assignment create another aerofoil by using different dat file for different aerofoil shapes.
Slide: Summary	In this tutorial we learnt: How To create an aerofoil in Gmsh. How to do meshing in Gmsh
Slide : About Spoken tutorials	Watch the video available at this URL: http://spoken-tutorial.org/What_is_a_Spoken_Tutorial It summarizes the Spoken Tutorial project. If you do not have good bandwidth, you can download and watch it.
Slide: About Spoken tutorials	The Spoken Tutorial Project Team -Conducts workshops using spoken tutorials -Gives certificates to those who pass an online test -For more details, please write to us contact@spoken-tutorial.org
Slide: Acknowledgement	Spoken Tutorials are part of Talk to a Teacher project, It is supported by the National Mission on Education through ICT, MHRD, Government of India. More information on the same is available at the following URL link http://spoken-tutorial.org/NMEICT-Intro
About the contributor	The script was written by Gautam Sharma and this is Rahul Joshi from IIT Bombay signing off. Thanks for joining.

Contributors and Content Editors

Gautam, Nancyvarkey