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GregJ April 8, 2013 06:06

3D sail CFD boundary conditions
I am new to OpenFoam and CFD generally. I have been running some examples (based on modified motorBike case) of a twisted wing sail.

I have had some success though with relatively small meshes as I run out of memory otherwise.

I have built a mesh around an .stl file and it runs ok and produces what seem like reasonable results (making no representation about the accuracy).

Now the issue I face is how to get the correct boundary conditions. I want to simulate the effect of atmospheric boundary layer (wind shear), vessel velocity and sheet angle on angle of attack. The angle of attack on sail varies along its span due to the effect of these. I want to be able to vary the inlet speed and direction and the vessel speed and direction (so I don't have to re-mesh for each run).

I have set up my mesh with the left hand an back walls as inlets and the right hand and front walls as outlet (the inlet direction will always be from the left and rear - i.e. starboard tack). This seems to work and allows me to generate a flow diagonally across the mesh.

First, question: Am I on the right track?
Second Question: How should I go about setting up the boundary conditions?

I can calculate a desired inlet vector at various heights using a half parabola then adding that to the vessel velocity vector. I am just not sure if this is the right approach and, if so, how to go about implementing it. My C++ knowledge is (so far) limited but I have some programming experience.

Thanks in advance.


vbchris April 8, 2013 22:30

Take a look at swak4foam and using the BC type groovyBC.
This is much easier to do than getting into programming and will solve many common BC issues.

It should let you use a math expression to set the appropriate inlet velocity profile.
One thought, can you rotate your sail so you can have only one inlet BC instead of 2. Then you can set the sides to cyclic and the far end to outlet.


GregJ April 8, 2013 22:48


Thanks for your response. I will take a look at swak4foam. I can rotate the sail but then this only represents s single operating angle. I wanted to avoid the need to remesh for each angle change.



GregJ April 21, 2013 21:11

I have attempted to install swak4foam with no success. I get warnings like "could not open file for source file FieldValueExpressionParser.yy" and errors like "no known conversion for argument 1 from ‘Foam::HashTable<const Foam::regIOobject*, Foam::word, Foam::string::hash>’ to ‘int’
make: *** [Make/linuxGccDPOpt/MeshesRepository.o] Error 1
Parser library did not compile OK. No sense continuing as everything else depends on it
Requirements for Library not satisfied. I see no sense in going on"

I have trawled through documentation and CFD online but this only confuses me more. I am using OpenFoam 2.2.0. I downloaded the tarball for swak4foam.

Any ideas of how I can progress through the maze?


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