Difference between revisions of "OpenFOAM/C3/Creating-and-Meshing-aerofoil-in-Gmsh/English"

• How to create an airfoil using Gmsh
• How to mesh the created airfoil

If not, for Gmsh kindly refer the tutorial on Installing and running Gmsh on the spoken tutorial website.

System Requirement

• Ubuntu Linux Operating system version 13.10. and
• Gmsh version 2.8.4

Aerofoils are streamline shaped wings which are widely used in airplanes and turbo machinery.

These shapes are such that the drag force is a very small as compared to the lift.

The dat file

Download the dat file and Python script

Open browser

Download the files

Go to desktop

We will download the .dat file and python script from this url:

http://community.dur.ac.uk/g.l.ingram/download.php

I will open the browser now.

In the address bar type in the url as shown in previous slide.

Download the naca5012xyz.dat file and the python script dat2gmsh.py and save on the desktop.

Go to the desktop. Here you can see both the files.

Open Python script

This file contains the calculated X and Y coordinates of each point that defines the airfoil.

We need the X, Y and Z coordintes in Gmsh acceptable format. This can be done manually but is time consuming.

We will use a python script to do it.

Let me show you the script.

This is the python script. Close the script.

In the terminal type cd space Desktop to change the present working directory to desktop.

Type ls and press enter. You can see both the files.

python dat2gmsh.py naca5012xyz.dat

This creates a new file with .geo extension which contains the coodinates in gmsh acceptable format.

The nac_lc is the characterstic length which is defined as 0.005

Zoom in at the tail

Close the gmsh

This opens the gmsh with the airfoil.

Zoom in by scrolling at the tail of the airfoil. You will note that the aerofoil has an open trailing edge.

Close the gmsh.

Add the point

We will add a new point at the tail to complete the aerofoil.

Type:

Point(1046) = { 1.005, -0.0005, 0.00000, nac_lc};

Open .geo file in gmsh

Spline(1000) = {1000:1046,1000};

Save and close the file.

In the terminal repeat the same command by pressing the up key. You will note that the edge is joined.

Enter the points as

(4 3 0)

(4 -3 0)

(-4 -3 0)

(-4 3 0)

Go to Geometry > Elementary entitites > Add and click on Points. Enter the coordinates of the boundary as:

(4 3 0)

(4 -3 0)

(-4 -3 0)

(-4 3 0)

Press e to end selection

Click e to end selection. We have our surface

Translate>extrude surface

Go to Translate and click on Extrude Surface.

Press e to end selection

Move the geometry

The Z component is kept as 1

Select the boundary of the surface.

Press e to end selection.

Use the left click of the mouse to move the geometry. You can see that the 3D geometry.

Go to Mesh>3D

Scroll down to Mesh and click on 3D. The mesh has been generated.

You may note that the mesh is finer near the airfoil and gets coarse as it goes towards the boundary.

We will name our file as airfoil.msh

Note that here msh stands for the file type mesh.

As an assignment try creating airfoil by using different dat file for different airfoil shapes.

• To create an Airfoil in Gmsh.
• To mesh in Gmsh.

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Acknowledgement

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