Oscillating residuals

rizwan4081 · April 12, 2020, 15:22

I am trying to perform a ventilation analysis of a tunnel with a source of fire inside it. I used the k epsilon and k omega SST for turbulence. Can please someone tell me the reason for this issue?k omegaSST.jpg

k epsilon.jpg

vinerm · April 13, 2020, 10:32

The residuals are not oscillating. You are running a transient case and the residuals are supposed to drop from rather high values to low values within each time-step. That's what you are observing.

rizwan4081 · April 14, 2020, 07:43

Understood. For a transient simulation I get peaks and troughs as it reaches convergence. But sometimes the trend of the oscillations are increasing in amplitude. And how can one judge the solution and say that the solution is converged?

vinerm · April 14, 2020, 08:16

Set up a few monitor points, such as, pressure, velocity, temperature, etc., at some boundaries. These should either achieve a constant value or a periodic oscillation in the value.

April 12, 2020, 15:22	Oscillating residuals	#1
rizwan4081 New Member Muhammad Rizwan Join Date: Mar 2020 Posts: 11 Rep Power: 6	I am trying to perform a ventilation analysis of a tunnel with a source of fire inside it. I used the k epsilon and k omega SST for turbulence. Can please someone tell me the reason for this issue?k omegaSST.jpg k epsilon.jpg

April 13, 2020, 10:32	Residuals	#2
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	The residuals are not oscillating. You are running a transient case and the residuals are supposed to drop from rather high values to low values within each time-step. That's what you are observing. RaiderDoctor likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

April 14, 2020, 08:16	Monitors	#4
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	Set up a few monitor points, such as, pressure, velocity, temperature, etc., at some boundaries. These should either achieve a constant value or a periodic oscillation in the value. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

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April 14, 2020, 07:43		#3
rizwan4081 New Member Muhammad Rizwan Join Date: Mar 2020 Posts: 11 Rep Power: 6	Understood. For a transient simulation I get peaks and troughs as it reaches convergence. But sometimes the trend of the oscillations are increasing in amplitude. And how can one judge the solution and say that the solution is converged?