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ravi August 24, 2004 10:44

drastic increase of temperature in one cell
 
hello,

In my problem at one cell alone there is a drastic increase of temperature as compared to other cells. can anybody tell me what may be the problem or how i can eliminate it.

thank you Ravi

Victor August 24, 2004 10:54

Re: drastic increase of temperature in one cell
 
Maybe the cell that you are referring to is skewed? In other words, the quality of the cell is really poor. /Victor

ravi August 24, 2004 12:43

Re: drastic increase of temperature in one cell
 
hello,

yea, the skewness is high but there are cells with much more skewness than this particular cell and which have not encountered any such kind of temperature rise problem. can anybody tell me how to eradicate my problem.

thanking you, ravi

Jason August 24, 2004 13:51

Re: drastic increase of temperature in one cell
 
Problems with skewness are amplified when they occur in areas of high gradients. If this cell occurs in an area where there's a lot going on, say separated flow or areas of high gradients, then the problem will be huge even if there are areas with worse skewness. I've also seen problems where certain turbulence models will cause a small part of the model to "blow-up" while other turbulence models don't have a problem with it. You can also try turning off the energy equation until you start to reach a reasonable solution. The skewness is probably the reason you're having the problem, but it's being amplified by what else is happening in your model.

Hope this helps, Jason

darin August 27, 2004 10:35

Re: drastic increase of temperature in one cell
 
Occasionally, ignoring the secondary gradient of temperature will help with the convergence. To turn it off issue the following command:

(rpsetvar 'temperature/secondary-gradient? #f)

Darin

ravi August 28, 2004 08:39

Re: drastic increase of temperature in one cell
 
Hi, Can u please eloborate where exactly should i give this command in FLUENT

darin August 29, 2004 19:52

Re: drastic increase of temperature in one cell
 
Simply type the command in the text-user-interface window.

(rpsetvar 'temperature/secondary-gradient? #f)

In response FLUENT will output to the text window

temperature/secondary-gradient?

Anton August 30, 2004 22:58

Re: drastic increase of temperature in one cell
 
Is this a transient or steady problem? If it's transient, try reducing the time step by an order of magnitude and see the temperature drops in that cell. You may also want to adapt that cell and some of its neighbours to give Fluent at better shot at calculating the gradients through there, if in fact they are high there.


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