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 eric October 8, 2003 13:05

Gravity and combustion

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

 Jin-Wook LEE October 9, 2003 08:11

Re: Gravity and combustion

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

 Colin October 9, 2003 17:27

Re: Gravity and combustion

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.

 Jin-Wook LEE October 9, 2003 23:45

Re: Gravity and combustion

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

 eric October 10, 2003 04:11

Re: Gravity and combustion

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

 Jin-Wook LEE October 12, 2003 21:43

Re: Gravity and combustion

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

 Narcis68 July 21, 2016 05:41

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?

Thanks in advance

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