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-   -   Meshing Techniques for Heat Transfer with Cube Shaped Objects (http://www.cfd-online.com/Forums/openfoam-meshing/83645-meshing-techniques-heat-transfer-cube-shaped-objects.html)

 cbritan January 6, 2011 05:06

Meshing Techniques for Heat Transfer with Cube Shaped Objects

I have been studying OpenFOAM for about 5 weeks now and I would like
some advice on which meshing technique best suits my needs. I will be
conducting simulations of temperature distribution in internal
environments with inlets and outlets blowing air and various cube shaped
objects in the room as heat sources (e.g. people and appliances). In a
given simulation there could be 10 vents and 20 heat sources. Eventually
I would to add heat transfer through walls as well. Below is a list of
what I have come up with as potential meshing techniques, but I am not sure
which technique I should use for the specified application:

1. blockMesh
This technique is easy to understand, but I believe it will require many
meshes in order to create the necessary patches. For example, I believe eight
meshes are needed in order to create a patch for each side surface of a cube.
Also, the number of vertices will become quite large for a full simulation.

2. Create the geometry in the snappyHexMeshDict
This is the technique used in iglooWithFridges. It is more difficult to
understand than blockMesh, but it if it will simplify mesh generation
then it will be worth the time.

3. Import a .stl file and use snappyHexMesh
application, then I will look into it further. Will it be difficult to
specify boundary conditions, such as the inlet air velocity of the
inlets (probable will model them as rectangular cubes with air blowing
out the sides) and the heat flux of the person cubes?

4. Import a mesh from third party software
I don't currently have access to any third party software, so I would
prefer not to use this technique. Also, for a purely rectilinear mesh I
don't think this is necessary.

Any suggestions for meshing techniques are welcome. Thank you for your
help.

-Clark

 chegdan January 25, 2011 21:17

Quote:
 Originally Posted by cbritan (Post 289441) I have been studying OpenFOAM for about 5 weeks now and I would like some advice on which meshing technique best suits my needs. I will be conducting simulations of temperature distribution in internal environments with inlets and outlets blowing air and various cube shaped objects in the room as heat sources (e.g. people and appliances). In a given simulation there could be 10 vents and 20 heat sources. Eventually I would to add heat transfer through walls as well. Below is a list of what I have come up with as potential meshing techniques, but I am not sure which technique I should use for the specified application: 1. blockMesh This technique is easy to understand, but I believe it will require many meshes in order to create the necessary patches. For example, I believe eight meshes are needed in order to create a patch for each side surface of a cube. Also, the number of vertices will become quite large for a full simulation. 2. Create the geometry in the snappyHexMeshDict This is the technique used in iglooWithFridges. It is more difficult to understand than blockMesh, but it if it will simplify mesh generation then it will be worth the time. 3. Import a .stl file and use snappyHexMesh I have access to CAD software, so if this is a good technique for my application, then I will look into it further. Will it be difficult to specify boundary conditions, such as the inlet air velocity of the inlets (probable will model them as rectangular cubes with air blowing out the sides) and the heat flux of the person cubes? 4. Import a mesh from third party software I don't currently have access to any third party software, so I would prefer not to use this technique. Also, for a purely rectilinear mesh I don't think this is necessary. Any suggestions for meshing techniques are welcome. Thank you for your help. -Clark
I use GAMBIT by ansys (proprietary 3rd party) since it is easy to use. One can use salome (http://www.salome-platform.org/about/mesh) or consult the list of links from cfd-online (http://www.cfd-online.com/Links/soft.html#mesh) Hope this helps.

Dan

 cbritan January 26, 2011 01:27

Thanks for the reply. I haven't looked into Salome yet, but I may try it out sometime.

I have found the geometry tool included in snappyHexMesh to be quite useful. I am able to create box shapes very easily and remove them from the mesh just like in iglooWithFridges. This creates a patch that includes all faces of the box and therefore makes it easy to specify the heat sources.

For the inlets, I am able to set the velocity and temperature of a portion of the ceiling, floor, or wall patches using funkySetFields fairly easily.

The question that remains is how to model the outlets for the room. Like with the inlets I am specifying using funkySetFields, I would like to specify outlet conditions as portions of the ceiling or floor patch.

Is there any easy way to do this, or do I have to specify an entire patch as an outlet?

Thank you for the help.

 chegdan January 26, 2011 16:16

Quote:
 Originally Posted by cbritan (Post 292189) Thanks for the reply. I haven't looked into Salome yet, but I may try it out sometime. I have found the geometry tool included in snappyHexMesh to be quite useful. I am able to create box shapes very easily and remove them from the mesh just like in iglooWithFridges. This creates a patch that includes all faces of the box and therefore makes it easy to specify the heat sources. For the inlets, I am able to set the velocity and temperature of a portion of the ceiling, floor, or wall patches using funkySetFields fairly easily. The question that remains is how to model the outlets for the room. Like with the inlets I am specifying using funkySetFields, I would like to specify outlet conditions as portions of the ceiling or floor patch. Is there any easy way to do this, or do I have to specify an entire patch as an outlet? Thank you for the help.
I haven't used funkySetFields beyond the cursory level, so I can't really say what it can do for you in this realm. I'm also not an expert on HVAC type problems. I would think that setting a portion of the ceiling as a separate patch and making it an outlet would be simple enough. You could aways try a few different methods and see if there was a difference...then compare to some experimental results. Anyway...not much help from me. Good luck.

Dan

 cbritan March 2, 2011 02:12

CastNet for OpenFOAM

I found the third party software called CastNet http://www.dhcae-tools.com/OpenFOAM.htm which I have found quite useful. Models can be importing in .stl, para solid, or asics formats. This software enables users to enter OpenFOAM specific parameters for nearly all of the built in solvers and it is done using a GUI. Meshing can be done by setting the snappyHexMesh parameters or with the internal meshing software of CastNet. Once all parameters are set and the mesh is created the software exports all of the input files required to run OpenFOAM. On the website it says the cost is less than 300 euros per month. So, other than the fact that it is not free;), this seems like the best option for me.

Does anyone have any other suggestions?

-Clark

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