Residuals Fluctuate after 3000 iter in inviscid

February 8, 2008, 12:56

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

February 8, 2008, 17:12

Make sure your mesh quality is good and if so try relaxing the solution to dampen out the residuals.

Carlos.

February 13, 2008, 11:43

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

satyendra · October 12, 2011, 00:04

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

February 8, 2008, 12:56	Residuals Fluctuate after 3000 iter in inviscid	#1
Shamoon Guest Posts: n/a	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

February 8, 2008, 17:12	Re: Residuals Fluctuate after 3000 iter in invisci	#2
Carlos Guest Posts: n/a	Make sure your mesh quality is good and if so try relaxing the solution to dampen out the residuals. Carlos.

February 13, 2008, 11:43	Re: Residuals Fluctuate after 3000 iter in invisci	#3
maxime Guest Posts: n/a	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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October 12, 2011, 00:04		#4
satyendra New Member satyendra Join Date: Jun 2010 Posts: 15 Rep Power: 15	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