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 VINEETH V K April 25, 2011 04:28

Operating Temperature....

hi,
I am working on a natural convection problem. When my operating temperature was 300 K or less than 300 K, i was getting a convergence of 10^-6 for mass, velocity& energy. But when my operating temperature was changed to above 300 K, say 304 my mass convergence became below 10^-6, where as the other variables are quite alright. I tried several ways( adjusting g, different schemes etc.). still i am not able to get a convergence for mass. can anyone suggest me a method or is it fluents incapability to capture the operating temperature more than 300K.

 xaero April 25, 2011 06:00

Hi Vineeth,
is your calculation stationary or instationary?

I have made some calculations with temp above 300K and there was no problem occuring

Some suggestions:
Try Body Force Weighted or PRESTO scheme

Instat. calculations are sometimes more stable than stationary ones, so you can try to calculate it instationary.

If you are calculating instationary, try to reduce the heat capacity and the density at the wall (try factor 1000)

greetings

 VINEETH V K April 26, 2011 00:22

hi sir,
we have tried the schemes. but still we are not able to get the convergence. can you give me some more suggestions. please tell me what is instationary problems. we are in urgent need of a solution for this problem.

 xaero April 26, 2011 01:36

Hello,
I meant that you should try to calculate transient, with a small time step and with a reduced density and heat capacity at the solid body.

greetings

 fierceyeo April 28, 2011 18:13

Hi, just one quick question, for solving natural convection, can I just use k-epsilon to solve, instead of using laminar. I find that k-epsilon can converge very fast and the result is reasonable

 xaero May 1, 2011 11:22

Hello fierceyeo,

it depends whether your case is laminar or turbulent, check your Ra number.

greetings

 skikay September 7, 2012 01:26

Quote:
 Originally Posted by VINEETH V K (Post 305047) hi sir, we have tried the schemes. but still we are not able to get the convergence. can you give me some more suggestions. please tell me what is instationary problems. we are in urgent need of a solution for this problem.
you take the following ways:
1.boussineaq,
2 set up thermal expansion index,
3 open gravity model and operation thermal.

i have tried the above ways and got a outstanding result.

 fangdian September 7, 2012 05:15

Quote:
 Originally Posted by skikay (Post 380669) you take the following ways: 1.boussineaq, 2 set up thermal expansion index, 3 open gravity model and operation thermal. i have tried the above ways and got a outstanding result.
hi,skikay
Which temperature is the operation temperature when i simulate the welding pool (the steel was heated and melt to welding pool) with the boussinesq model? the solidus temperature or the liquidus temperature ?
Or i have to set other temperature as the operation temperature?
thanks:p

 skikay September 7, 2012 07:38

Quote:
 Originally Posted by fangdian (Post 380698) hi,skikay Which temperature is the operation temperature when i simulate the welding pool (the steel was heated and melt to welding pool) with the boussinesq model? the solidus temperature or the liquidus temperature ? Or i have to set other temperature as the operation temperature? thanks:p
i don"t know your case, when i cmpute the nature thermal convection,the lowest temperature is regard as operation temperature.

 nenazarian September 7, 2012 16:35

Quote:
 Originally Posted by skikay (Post 380717) i don"t know your case, when i cmpute the nature thermal convection,the lowest temperature is regard as operation temperature.
Hi

I have a streamwise periodic boundary condition and Im also using solar load model with Do radiation. Im also accounting for buoyancy and used boussinesq approximation.

In my case, I defined the operating temperature to be the same as bulk stream temperature that is entering the domain.
However, since the solar calculator works with a shading algorithm, the lowest temperature in the domain would be less than bulk stream temperature. (and this is something that I get after simulation)

So how should I know that Im putting a correct value as operating temperature and how will it effect my solution??!
Should I be concerned?

I would appreciate if you advise me on this.

Cheers
Negin

 skikay September 7, 2012 20:27

Quote:
 Originally Posted by nenazarian (Post 380801) Hi Im confused about applying your statement to my case. I have a streamwise periodic boundary condition and Im also using solar load model with Do radiation. Im also accounting for buoyancy and used boussinesq approximation. In my case, I defined the operating temperature to be the same as bulk stream temperature that is entering the domain. However, since the solar calculator works with a shading algorithm, the lowest temperature in the domain would be less than bulk stream temperature. (and this is something that I get after simulation) So how should I know that Im putting a correct value as operating temperature and how will it effect my solution??! Should I be concerned? I would appreciate if you advise me on this. Cheers Negin
when you simulink your model, the temperature in initialize dialoge box is the same as operature temperature.
so according to this,when i compute my radiation case,always i got an excellence results.plz try again!

 nenazarian September 7, 2012 20:48

Quote:
 Originally Posted by skikay (Post 380813) when you simulink your model, the temperature in initialize dialoge box is the same as operature temperature. so according to this,when i compute my radiation case,always i got an excellence results.plz try again!
initial temperature doesnt have any effect in my case.
Im not sure what you are asking me to try right now!

Cheers
Negin

 enayath August 8, 2014 10:16

Negin,

Could you figure it out how to set up the value of the operating temperature?
I am working on natural convection...two different temperatures as my BCs(300K and 320K)...using Boussinesq approximation...not sure how to find the correct value of operating temperature...
Using 310K to initiate the calculation...

Thanks,
Hooman

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