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Abnormal Temperature Value in Running(FloEFD)

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Old   May 16, 2018, 04:45
Unhappy Abnormal Temperature Value in Running(FloEFD)
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Vasif Can YILDIRAN
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Dear all,

I'm trying different form of propeller in close system with one heater(like oven). All form is same but only I change propellers.

I have good results for five different propellers(five different analysis) but another one made a problem. The problem is abnormal temperature value. It is running but after 25-30 iterations max temperature(resistance) go on abnormal values (like resistance temp:500 C but analyze have got 3000 C). And we know that it is impossible that max temperature to exceed resistance temperature.

Have you ever face this problem? Have you got some ideas for me?

Thanks,
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Old   June 27, 2018, 11:19
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Boris Marovic
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Hi Vasif,

if the mesh is 100% the same (no refresh mesh setting message appeared and mesh wasn't changed) and the hot temperature is not at the region of the changed geometry, then it is hard to tell from your post.
But if your mesh settings are set to automatic settings and you changed the geometry, the automatic mesh might change the mesh slightly in the whole model and you experience one weird cell causing the temperature to spike and run crazy near that cell. Best thing to do is to deactivate the automatic mesh and add 1 cell in x, y and z-direction so the whole mesh is slightly changed and that cell is moved in any direction and not at the same spot anymore.
This can happen every now and then, often accompanied with the message for high Mach number flow as that cell for some reason causes abnormal values. It just sits not nice on the geometry, usually a cell that intersects the fluid/solid boundary.

Try if this helps.
Boris
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Old   June 29, 2018, 04:49
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Hi Boris,

Thanks for your answering. I solved the problem with little bit more fine mesh. Actually, ı used same geometry without propeller and same mesh(same but not automatic). I didn't understand clearly what is the problem but ı think that mesh number was low number to solve it and it had problem to converge it.
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Old   June 29, 2018, 05:13
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Boris Marovic
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Hi Vasif,

Yes, too few cells of course can influence the convergence as fluctuations are occurring easier with too big gradients between the cells. But rotation such as in pumps and fans can take longer to converge as there might be fluctuations in the mass flow or pressure and it takes a little bit longer till they converge.
It is wise to monitor the goals and see if they actually converged or if the simulation stopped automatically because it has reached the default setting of 4 travels. In this case it is better to deactivate the limitation of the travels and let it run longer. This default is mostly set as most simulation don't take 4 travels to converge but in case some are having issues to converge and you have other projects in the queue, they will not start until the previous project has stopped. So that setting will at some point stop it automatically.

Boris
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Old   June 29, 2018, 05:33
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Vasif Can YILDIRAN
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I understand Boris. I will remember these when ı have a problem like this.
Thank you for your help.

Regards
Vasıf
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