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buoyantSimpleRadiationFoam is missing in OF v2.2.2

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Old   February 4, 2014, 10:56
Default buoyantSimpleRadiationFoam is missing in OF v2.2.2
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Cong
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Hi Foamers,

I found the solver buoyantSimpleRadiationFoam missing in the latest OF version 2.2.2. Does anybody know what happend and why?

Thank you.
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Old   February 5, 2014, 03:17
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Tom Fahner
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Hi,

Radiation is now automatically included in the heat transfer solvers. So you can use buoyantSimpleFoam and choose a radiation model there. If you want to solve without radiation just use the 'none' model.

Regards,
Tom
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Old   February 6, 2014, 15:59
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Quote:
Originally Posted by tomf View Post
Hi,

Radiation is now automatically included in the heat transfer solvers. So you can use buoyantSimpleFoam and choose a radiation model there. If you want to solve without radiation just use the 'none' model.

Regards,
Tom

Thank you Tom.

I am still wondering why radiation is not included in buoyantBoussinessqSimpleFoam?

If I want to simulate natural convection, how can I include the effect of radiation if I don't to want to use buoyantSimpleFoam?

[...]

I am wondering the reason why why radiation is not included in buoyantBoussinessqSimpleFoam.

If I want to simulate a natural convection, how can I include radiation if I don't use buoyantSimpleFoam?

Thank everybody!

Last edited by wyldckat; February 6, 2014 at 18:18. Reason: merged two posts, since they were posted 2 minutes apart
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Old   February 6, 2014, 18:39
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Bruno Santos
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Greetings to all!

I don't know for certain, but it's possible that the radiation model might not be implemented in OpenFOAM 2.2 either because:
  • There were no test cases that could be used for validating its implementation.
  • OpenCFD did not have any clients that needed it.


Anyway, I spotted the other day that Symscape's patches for their port of OpenFOAM 2.2.x for Windows: http://www.symscape.com/openfoam-2-2-x-on-windows - have got the aforementioned radiation model implemented in the solver buoyantBoussinesqSimpleFoam.

Attached is an excerpt of their patches, which only has the patch for the solver alone. To use it, follow these steps:
  1. Download the attached file "buoyantBoussinesqSimpleFoam_with_radiation.patch. gz" and place it inside the folder where OpenFOAM is installed.
  2. Run these commands:
    Code:
    gunzip buoyantBoussinesqSimpleFoam_with_radiation.patch.gz
    patch -p0 < buoyantBoussinesqSimpleFoam_with_radiation.patch
    ./Allwmake
  3. It will take a while to build and when it's complete, it should be ready to be used.
Warning: These instructions assume that you have build OpenFOAM from source code.

Best regards,
Bruno
Attached Files
File Type: gz buoyantBoussinesqSimpleFoam_with_radiation.patch.gz (706 Bytes, 12 views)
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Last edited by wyldckat; February 6, 2014 at 18:39. Reason: had forgotten to attach the file
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Old   February 7, 2014, 03:25
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Tom Fahner
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Hi,

My guess would be that radiation with Boussinesq assumption would be rarely valid. Since for radiation to be important you need large temperature differences, which makes the Boussinesq approach inaccurate. Also the radiation models result in an energy source and not in a temperature source, while buoyantSimpleFoam solvers for energy or enthalpy and buoyantBoussinesqSimpleFoam solves for temperature. I guess there is some programming needed to combine everything like Bruno pointed out.

Regards,
Tom
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Old   February 10, 2014, 15:39
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Chris Sideroff
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Simply saying large temperature differences for radiation can be misleading and there are radiation cases where the Boussinesq approximation is valid.

To demonstrate, one can use the following equations to estimate the magnitude of radiation's contribution to the heat transfer

q_{rad} = \sigma\left(T_{wall}^4 - T_{ref}^4\right)\;\frac{W}{m^2}

versus convection:

q_{conv} = h\left(T_{wall} - T_{ref}\right)\;\frac{W}{m^2}

Now compare temperature difference versus heat flux for both. You'll find the relative contributions depend on h, for convection, and T_{ref}, for radiation. See the plot I quickly threw together where I plot q_{conv} for two values of h and q_{rad} for two values of T_{ref}. (note: in the legend I used Celsius but I did the calculation with Kelvin.)

For small values of h or large values of T_{ref} their relative magnitudes are close. So relative to convection, the importance of radiation depends on the convective heat transfer coefficient, the absolute level of temperature or both. Even though the Boussinesq is valid for \beta \Delta T << 1 there are situations where it's valid to use it with radiation (left half of the plot).

My point is the importance of radiation is a little more complicated than simply saying only for large temperature differences. Additionally, radiation can be important for heat transfer problems even if the radiative contribution from the gas is negligible.

-Chris

Quote:
Originally Posted by tomf View Post
Hi,

My guess would be that radiation with Boussinesq assumption would be rarely valid. Since for radiation to be important you need large temperature differences, which makes the Boussinesq approach inaccurate. Also the radiation models result in an energy source and not in a temperature source, while buoyantSimpleFoam solvers for energy or enthalpy and buoyantBoussinesqSimpleFoam solves for temperature. I guess there is some programming needed to combine everything like Bruno pointed out.

Regards,
Tom
Attached Images
File Type: jpg conv-vs-rad.jpg (39.8 KB, 23 views)
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Last edited by cnsidero; February 11, 2014 at 09:39.
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