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Old   September 1, 2013, 01:02
Default residual
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Dear All
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Please find attached file, Results obtained after 715 iteration. As can be seen, the residual curve for some equation is above 1 (about 100). If the residual graph is higher than 1, what can be concluded? Does the model have a problem?
residual.JPG
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Old   September 1, 2013, 12:08
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go to monitor option and go to normalization and instead auto u put as off..after that u check that its less than 1 or not.........if not less than 1 it means problem in ur set up.............
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Old   September 2, 2013, 03:08
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Actually, I don't think that this looks bad at all. It looks like your values converges well, what you should look out for are sudden "spikes" in your residuals that can push your solution in a divergence state.

Also, taken from manual:

"In general, use normalized residuals to monitor the behavior of the solvers at each iteration to make sure that the solution is converging toward the machine precision. If the simulation is steady state, the convergence is displayed over the total number of iterations. If the solution is time-dependent, make sure that convergence occurs within each time-step."
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Old   September 2, 2013, 06:20
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If this is a transient simulation, decrease the time step size and increase the number of iterations per time step.
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Old   September 7, 2013, 10:40
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Dear all,
thank you for your help
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Old   January 29, 2014, 09:46
Default Problem with residuals -- Sudden jump
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Hello all
I have been experiencing similar problem. The thing is .. I have sudden jumps in the residual especially for Tdr ... !

Also Tdr residual(normalization off) starts at 100 and decreases to 0.1 in 10 iterations and then every 40-50 iterations it jumps to 100 again and then starts decreasing for next 40-50 iterations and then again jumps to 100 ... this continues ... !! Rest all residuals are smooth and keep reducing ... in the order of 1e-5 or so .. ! only Tdr is oscillating above 1 or so .. !

I cannot figure out what is going on ... if there is mistake in my problem set up ... it would be very helpful if some one can give me some hints what could be wrong .

Thank you in advance
Aditya
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Old   February 6, 2014, 20:39
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Typically this occurs with an incorrect near-wall spacing or with incorrect inlet/initial turbulence values.
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Old   March 11, 2014, 13:15
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you can try to reduce the Under relaxation factor (URF) of turbulence solver to 0.5 or 0.4.
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