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December 21, 2018, 12:53
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Domain Imbalance
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#1 |
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New Member
Join Date: Nov 2018
Posts: 15
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Hi everybody
I'm doing some simulations on a Transonic stage, with the 500k-target mesh for both rotor and stator. After 10000 iterations the Domain imbalance for the Energy term is still over 0.01, so I was wondering: should I continue iterate to reach that limit or I can assume the solution as converged? |
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December 21, 2018, 16:50
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#2 |
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Senior Member
Gert-Jan
Join Date: Oct 2012
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Compared to the other terms, the imbalance of 0.1779 is very small. So, why should you continue?
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December 21, 2018, 18:12
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#3 |
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New Member
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Well, since I'm relatively new to CFD it's something I wasn't 100% sure about it, I had a domain imbalance of roughly for the stator 5E1 and since the usual criterion is <0.01 I was afraid that was a mistake to leave the simulation as it was
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December 21, 2018, 18:20
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#4 |
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Senior Member
Gert-Jan
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0.01 is relative and equals 1%. I guess you already reached that long time ago.
But it is good practice to tighten this convergence criterium. So keep up the good work! |
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December 21, 2018, 18:23
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#5 |
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New Member
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Actually, this doubt aroused this morning due to the residuals: for a problem I had in the model, there is a recirculation zone in the stator zone that doesn't allow the solution to converge properly. I checked the efficiency monitor and it was oscillating. I then changed the timestep model and it was still showing a small oscillating tendency, so I was wondering if the imbalance was still too high to have a better converged efficiency
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December 21, 2018, 18:27
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#6 |
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Super Moderator
Glenn Horrocks
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This looks very similar to the FAQ: https://www.cfd-online.com/Wiki/Ansy...gence_criteria
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum. |
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December 21, 2018, 18:32
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#7 |
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Senior Member
Gert-Jan
Join Date: Oct 2012
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I would be happy to obtain results like that. Mostly my cases lead to more chaos. ;-)
In your case, it is likely CFX can't find a stable solution, resulting in a oscillating flow solution. Depending on the origin of the oscillation, it sometimes helps to increase the time step by a factor 10, or decrease by a factor 5. Difficult to say. If the origin is a real transient phenomena, then switch to transient. |
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December 21, 2018, 18:34
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#8 |
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New Member
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To tell you the truth I haven't enough time to do a transient simulation, I will try to do the best with what I have now
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December 21, 2018, 18:36
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#9 | |
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New Member
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Quote:
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