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Residuals Fluctuate after 3000 iter in inviscid

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Old   February 8, 2008, 13:56
Default Residuals Fluctuate after 3000 iter in inviscid
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Shamoon
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Hi all, I am running a problem of an aircraft on FLUENT 6.3. I am running inviscid model. The mesh size is i.7 Million. The problem is that for the first 3000 iterations the resiudals go smooth and then ALL(x, y, z velocitites energy) residuals start Fluctuating with very small amplitude. with 10 i peak per iteration I cant undersand wats the reason for that because solution is not going to converge even after 5000 itr. The problem was run on Parallel
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Old   February 8, 2008, 18:12
Default Re: Residuals Fluctuate after 3000 iter in invisci
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Carlos
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Make sure your mesh quality is good and if so try relaxing the solution to dampen out the residuals.

Carlos.
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Old   February 13, 2008, 12:43
Default Re: Residuals Fluctuate after 3000 iter in invisci
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maxime
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Are you using a steady-sate model or a time dependent? If you're using a time dependent, the oscillations can be caused by numerical diffusion. The way to avoid these fluctuations consists in adaptin' time step in function of the general display of residuals. but if you're using a steady state model, I don't really know how to help you
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Old   October 12, 2011, 00:04
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satyendra
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hi maxime,

i am doing analysis of a furnace in fluent 6.3(geometry modeled in gambit 2.24). i have made structured mesh in most of the volume except at the corners of the mould.

initially when the hot gases' velocity were low it was converging, but i was not getting required temperature inside mould. hence i increased the flow rate without changing the model.

But now except energy, all other residuals i.e continuity, k, x, y, z velocity and epsilon are fluctuating. following are the specs:
1. unsteady flow.
2. turbulent k-epsilon and RNG model
3. time step = 1

thanks
satyendra
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