negative index in product of combustion

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Nay Robin

Nay Robin

June 26, 2013 1:26am UTC

negative index in product of combustion

Hi everyone,

Im tryin to simulate combustion in combustion chamber. the fuel is gas pyrolysis (ch4, c2h6, h2, and co) it enter the domain from the bottom of the chamber. i also have air input which comes into chamber from holes at the side of chamber.

i use 3 interfaces :
-heat transfer in fluid
-turbulent k-e
-transport in diluted species

the problem is, concentration result seems so unlogic because there are some spot where the reactant increase and also only a little spot the product exist. and the product is decrease.

hopefully anyopne could help me to get out from this problem.

thank you

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Tero Hietanen

Tero Hietanen

June 26, 2013 7:19am UTC in response to Nay Robin

Re: negative index in product of combustion

Hi,

I have noticed same problem with concentration. Usually high concentration is coming to places were flow is rotating at one place. Also there could be numerical errors from coarse mesh.

Low concentration near walls is coming from wall function. k-epsilon turbulence wall function cannot handle concentration flow in/out of wall area. Due to this material which is going inside to wall function area is disappearing. One solution could be to use "slip" condition to walls.

New Comsol 4.3b is containing EDC (EDM) model. Model contains functions how to handle wall function and concentration.

Best regards

Tero Hietanen

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Nay Robin

Nay Robin

June 27, 2013 12:07am UTC in response to Tero Hietanen

Re: negative index in product of combustion

Hi tero,

Thank you for your answer. i tried to use slip wall but i cant get convergence for my diluted species interface. and i dont know why. does the solver influence convergence? my study is stationer. then i use fully-coupled-double dogleg because i read that this solver special for stationar study but the error come down slowly. then i try to use fully-coupled-automatic (newton) as a default, then i didnt get any convergence. the convergence is fluctuative.

thank you

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