windgen.org vawt discussion

The do script needs the name of the .geo file.  So if the .geo file is called turbine.geo, then then start the do script with 'do turbine'.

I've posted a complete example of how to simulate a turbine with OpenFOAM-1.5-dev and gmsh at this location:  HERE

The link is a compressed tar file with the complete case.  The 'do' script shows you how to execute the simulation.

I'm getting quite a few requests for this information so I'm going to put together a web page on some openfoam basics.

Awesome! What I could really use is would be some very simple step by step procedures for getting this far in Foam. It looks so powerful that I would probably spend 6 months to get to this point. Do you know of any simple example/procedures that might be helpful?

Since at least one of you has shown an interest in using openfoam, I thought I'd show the mesh used to run one of my simulations.

These are screenshots from a program called gmsh.  Found here

Gmsh is a program that lets you generate meshes for finite element analysis like mechanical stress analysis or air flow simulation.  You can either sketch your objects or describe them with a kind of language.  I always use the language because I can go back, edit a few lines and change  things without redoing a lot of work.

This first shot is my whole wind tunnel.  It's 8m x 8m.  If it were real it would take up most of my house.  The mesh size at the edges is 40cm, which is very large.  This saves computer time and that area isn't very important since the air just moves in a straight line at the edges.  It's necessary to have a large wind tunnel because if the tunnel is too small the walls affect the airflow over the turbine.





This next shot is zoomed in on my rotating mesh.  There are two different meshes.  The outside one which stays still, and the inside circle which I rotate to simulate a turbine turning.   There is a small gap (.5mm) between the two meshes, but the software knows to join the airflow from one to the other.  When the mesh is rotated during simulation, the actual air movement in that mesh is counter rotated so it keeps going in the same direction.  The mesh size at the rotational border is about 1 cm.



This next shot is zoomed in a little more.  It shows the rotational border, the blade and the pole in the middle.   At this point you will notice that objects like blades and poles are just holes in the mesh.  They are places where the air can't flow.  That's all.



Finally this is a zoomed view of the blade.  I usually make the mesh size on a blade between 2 and 4 mm, depending on how long I want to wait for the simulation to run.  The finer the mesh the longer it takes, but the more accurate the simulation is.  This is true, especially if there are sharp corners or tight curves.



There are all kinds of things I had to do to make these meshes work in openfoam.   Certain areas had to be given certain labels, etc.)  It took over a month to learn how to do it.   But now I have a gmsh 'program' that does it all.  I just describe the blade shape in terms of points, lines, and curves.  I set a few parameters at the beginning of the file for the number of blades, attack angle, radius, etc and it constructs the mesh.   If anyone is interested in meshing your own projects, please get this file from me and save yourself a month of work.

Openfoam comes with a meshing program (Blockmesh) but it is terrible to use.  It's almost impossible to describe something like a turbine blade.  I highly recommand gmsh.  All the software I use is public domain and free.

If anyone is interested in making their own mesh, I'd be happy to run the simulation on it for them.


-- Edited by sjh7132 on Thursday 14th of January 2010 05:50:43 PM

-- Edited by sjh7132 on Thursday 14th of January 2010 05:52:28 PM

-- Edited by sjh7132 on Thursday 14th of January 2010 05:53:08 PM

-- Edited by sjh7132 on Thursday 14th of January 2010 05:54:50 PM

-- Edited by sjh7132 on Thursday 14th of January 2010 06:08:22 PM