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Old   October 8, 2003, 13:05
Default Gravity and combustion
  #1
eric
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Hi,

Can anyone tell me where gravity is accounted for in the non-premixed combustion and species transport tutorials?

I can't see how the gravity is accounted for in these tutorials. Does this mean that gravity effects can be neglected in combustion type simulations?

Regards,

Eric
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Old   October 9, 2003, 08:11
Default Re: Gravity and combustion
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Jin-Wook LEE
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You can account for gravity by activating 'GRAVITY' in 'DEFINE->OPERATING-CONDITION', if you need.

In general, in large system(or high Re, or large flame...), gravity(buoyancy force effect) can be neglected. You can check it by Richardson number, Gr/Re^2. Re : Reynolds number, Gr : Grashof number.....

Sincerely, Jinwook
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Old   October 9, 2003, 17:27
Default Re: Gravity and combustion
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Colin
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Hi,

You could refer your question to mine that posted by me: Gravity (g) Influence on Simulation Results

By the way, for the tunnel fire studies, I was convinced by Steve that even if the tunnel was horizontally placed, the gravity still play a role in your final results.

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Old   October 9, 2003, 23:45
Default Re: Gravity and combustion
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Jin-Wook LEE
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I agree with you for tunnel case.

For very large combustor, e.g., furnace of fossile power plant, the effect of gravity is fairl small. Anyway, gravity affects the results, negligible for somecase, fairly for certain cases, or sometimes very significantly.

Sincerely, Jinwook

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Old   October 10, 2003, 04:11
Default Re: Gravity and combustion
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eric
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Thanks for the reply.

What about a 1m long kiln of 0.5m diameter, Do you think gravity will have an effect on the flow in this case?

Also, I know that the gravity acts in the y direction in my model but do you apply the direction, i.e. -y, as well?

Thanks

Eric
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Old   October 12, 2003, 21:43
Default Re: Gravity and combustion
  #6
Jin-Wook LEE
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Anybody can say that gravity affects the results. But nobody can say that gravity can be neglected, because it's dependent of the system which you are going to solve. Unfortunately, what I can say is, it should be decided by yourself. I recommend that you would compare two results with and without gravity for the first case.

Direction of gravity is dependent of your modeling(meshing). + or - is only the direction.

Sincerely, Jinwook

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