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

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.

Contributors and Content Editors

PoojaMoolya, Pratik kamble, Sandhya.np14