# Gravity and combustion

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 October 8, 2003, 13:05 Gravity and combustion #1 eric Guest   Posts: n/a 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

 October 9, 2003, 08:11 Re: Gravity and combustion #2 Jin-Wook LEE Guest   Posts: n/a 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

 October 9, 2003, 17:27 Re: Gravity and combustion #3 Colin Guest   Posts: n/a 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.

 October 9, 2003, 23:45 Re: Gravity and combustion #4 Jin-Wook LEE Guest   Posts: n/a 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

 October 10, 2003, 04:11 Re: Gravity and combustion #5 eric Guest   Posts: n/a 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

 October 12, 2003, 21:43 Re: Gravity and combustion #6 Jin-Wook LEE Guest   Posts: n/a 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

July 21, 2016, 05:41
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Narges
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Quote:
 Originally Posted by Jin-Wook LEE ;108399 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
Hi
i am modelling a curved micromixer. and i'm not sure to account gravity or not.
i can not see gravity in the equations written in the paper.
but it seems without it the contours look different in comparison with those of paper's.
how should i explane the reason why i used gravity in this case?
can anybody help?