OpenFOAM/C3/Creating-and-Meshing-aerofoil-in-Gmsh/English-timed
From Script | Spoken-Tutorial
| Time | Narration |
| 00:01 | Hello and welcome to the spoken tutorial on Creating and Meshing aerofoil in Gmsh. |
| 00:08 | In this tutorial, we will learn how to create an aerofoil using Gmsh |
| 00:14 | and mesh the created aerofoil. |
| 00:17 | As a prerequisite, the user should have knowledge of aerofoil and Gmsh. |
| 00:23 | If not, for Gmsh, please see the tutorial on Installing and running Gmsh on the spoken tutorial website. |
| 00:31 | To record this tutorial, I am using:
Ubuntu Linux Operating system version 14.04 and Gmsh version 2.8.3 |
| 00:42 | Let me introduce you to aerofoil. |
| 00:45 | Aerofoils are streamline shaped wings which are used in airplanes and turbo machinery. |
| 00:53 | These shapes are such that the drag force is a very small fraction of the lift. |
| 00:59 | This is a picture of an aerofoil. |
| 01:03 | The predefined coordinates for aerofoil are available in simple text file with ".dat" extension. |
| 01:11 | I will download the .dat file and Python script from this url: |
| 01:19 | Let me open the website. |
| 01:22 | Download the .dat file and the Python script and go to the Downloads folder. |
| 01:31 | Copy and paste both these files on the Desktop from the Downloads folder. |
| 01:37 | Open the .dat file. |
| 01:40 | This file contains the calculated X and Y coordinates for each point that defines the aerofoil. Z coordinate is kept as zero. |
| 01:51 | We need the X, Y and Z co-ordintes in Gmsh acceptable format. |
| 01:56 | This can be done manually but this is time consuming. |
| 02:01 | Now open the Python script. |
| 02:04 | This Python script converts the data in the .dat file and gives the output in a separate file which is understood by Gmsh. |
| 02:14 | Now open the Terminal window. Type: cd space Desktop. |
| 02:21 | Now type: python space dat2gmsh.py space, the name of the dat file and press Enter. |
| 02:31 | Now type ls. We can see that a new file by the name naca5012xyz.dat .geo will be generated. |
| 02:43 | Open the geo file. |
| 02:46 | This contains the co-ordinates in Gmsh format. |
| 02:50 | Here, nac_lc is the characteristic length which is defined in the first line as is 0.005. |
| 02:59 | I will change this to 0.5. |
| 03:03 | This is because we require a coarser mesh. |
| 03:07 | You can change this value according to your mesh requirement. Now save this file. |
| 03:15 | In the terminal window, type: gmsh space, name of the geo file and press Enter. |
| 03:25 | This opens gmsh with the aerofoil. |
| 03:29 | Now, zoom in by scrolling at the tail end of the aerofoil. |
| 03:35 | You will note that the aerofoil has an open trailing edge. |
| 03:40 | Close gmsh. Now go back to the geo file. Scroll down. |
| 03:48 | We will add the last point and join it. |
| 03:53 | Now, above spline, enter Point open close bracket 1046 space = open close curly bracket space 1.005 comma space -0.0005 comma space 0.00000 comma space nac_lc close it with a semicolon. |
| 04:26 | Modify the spline as Spline(1000) = curly braces open 1000 colon 1046 comma 1000 close the curly bracket semicolon. |
| 04:44 | Save the geo file. |
| 04:47 | Now, open the modified file in Gmsh. We can see that the edge is joined. |
| 04:56 | Now we will make a boundary around the aerofoil using points. |
| 05:02 | Enter these coordinates 4, 3, 0 and change the prescribed mesh element size to 0.5 . Press Enter. |
| 05:17 | Similarly, add the other points.
4 -3 0 -4 -3 0 -4 3 0 |
| 05:29 | Now, join the points with a straight line. |
| 05:44 | Now click on Plane surface and select the surface boundary. |
| 05:52 | Zoom-in and select the aerofoil as the hole boundary. |
| 05:58 | Press e to end selection. You can see we have our surface. |
| 06:04 | Now, we will extrude the surface to make it 3D. Go to Translate >> Extrude Surface. |
| 06:14 | A new window will appear asking for the coordinates for translation. |
| 06:19 | Since we want to extrude the surface in Z direction, enter the coordinates for Z direction as 1.
And, click on the boundary of the surface. |
| 06:30 | Press e to end selection. |
| 06:33 | Use the left click of the mouse to move the geometry. |
| 06:37 | You can see that the geometry has been extruded. |
| 06:42 | Close this. Close the gmsh window. |
| 06:45 | Open the geo file. |
| 06:48 | Scroll down and go to Extrude. |
| 06:52 | Inside Extrude, add these lines:
Layers{1}; Press Enter. Recombine; Save this file. |
| 07:09 | This will ensure that the mesh is one element thick. |
| 07:14 | Now, in the terminal window, open the geo file. |
| 07:19 | Now we have our geometry, we will do the meshing. |
| 07:23 | Gmsh automatically generates the mesh for the defined geometry. |
| 07:28 | Go to Mesh. |
| 07:30 | Click on 1D mesh, 2D mesh and 3D mesh. |
| 07:36 | The mesh has been generated. |
| 07:39 | You may notice that the mesh is finer near the aerofoil and gets coarser as we move towards the boundary. |
| 07:48 | We can also refine the mesh by clicking on the Refine by Splitting parameter in the mesh menu. |
| 07:56 | Now, let us save our work. |
| 07:59 | Go to File menu and click on Save as. |
| 08:05 | A new window will appear. In the drop down, change to the mesh format. |
| 08:11 | And type the name of the file as aerofoil.msh. |
| 08:17 | Note that here msh stands for the file type mesh. |
| 08:22 | Click OK . Again click OK. |
| 08:26 | This brings us to the end of the tutorial. |
| 08:29 | As an assignment, create another aerofoil by using different dat file for different aerofoil shapes. |
| 08:37 | In this tutorial, we learnt:
How to create an aerofoil in Gmsh. How to do meshing in Gmsh. |
| 08:45 | Watch the video available at this URL.
It summarizes the Spoken Tutorial project. |
| 08:52 | If you do not have good bandwidth, you can download and watch it. |
| 08:56 | The Spoken Tutorial Project team: Conducts workshops using spoken tutorials. |
| 09:00 | Gives certificates to those who pass an online test. |
| 09:03 | For more details, please write to us at:contact@spoken-tutorial.org |
| 09:06 | Spoken Tutorials are part of Talk to a Teacher project. |
| 09:09 | It is supported by the National Mission on Education through ICT, MHRD, Government of India. |
| 09:15 | More information on the same is available at the following URL:http://spoken-tutorial.org/NMEICT-Intro |
| 09:19 | The script was written by Gautam Sharma and this is Rahul Joshi from IIT Bombay, signing off. Thanks for joining. |
