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Is the radiation solution correct?

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Old   December 22, 2003, 13:22
Default Is the radiation solution correct?
  #1
Jonathan
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Hello All,

Does anyone have experience with Radiation Models in CFX 5.6? I am trying to incorporate Radiation into my model, but I am not certain I am doing things correctly:

1. How do I know if the radiation equations are converged? The solver outputs values called %lost and %imbal. What are these values and why do I care about them? Should %lost eventually go to zero?

2. Can the Discrete Transfer model be used for a pure surface to surface problem (absorption coefficient=0)? It seems to give more reasonable answers than the Monte Carlo method.

Thank you for any suggestions,

Jonathan
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Old   December 22, 2003, 22:28
Default Re: Is the radiation solution correct?
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Neale
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Jonathan,

%lost is the percentage of rays lost by the radiation tracker. Usually this number will be zero. However, in certain cases it can be a small number greater than zero. If it get's much larger than a few percent you will not be conserving energy and you should be careful about interpreting your answers. i.e. if you loose a ray somewhere then the energy carried by that ray goes off into never-never land.

I'm not 100% certain about %imbal, but it likely has to do with how well "balanced" the radiation equation is. i.e. how close do all the boundary radiation flows and sources add up to zero.

I don't think that DTM is a valid model for zero optical thickness (or absorption coefficient). Monte Carlo should give you better answers for surface to surface type problems. Perhaps you just need to use more photons?

Neale
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Old   December 23, 2003, 03:02
Default Re: Is the radiation solution correct?
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Pascale Fonteijn
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For MC use more fotons (>1M) and probably a lower value for the Target Coarsening Rate.

Pascale
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