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-   -   Moving Reference Frame (http://www.cfd-online.com/Forums/fluent/44927-moving-reference-frame.html)

lila June 5, 2007 06:03

Moving Reference Frame
 
I try to represent mixing in a oval reactor, so I used the MRF for the fluide with a rotational speed of 5rad/s (first simulation). and a moving wall with rotational speed 0rad/s in the absolute reference frame. the probleme that when I used the K-e model (the flow is turbulente). I introduce a turbulente intensity and length scale on the inlet and outlet but no condition at the agitator. fluent give message "turbulent viscosity limited to viscosity ratio of 1.000000e+005 in 4194 cells" thanks in advance for the answer


Rams June 5, 2007 08:11

Re: Moving Reference Frame
 
the problem u have is that turbulent viscosity in 4194 cells is exceeding the limit,

if the number of cells ( i.e 4194 ) in which turbulent viscosity limited to viscosity ratio of 1.000000e+005, decreases as the solution progresses then u can carry on,

if it goes on increasing, try to increase the viscosity ratio limit,


lila June 7, 2007 09:03

Re: Moving Reference Frame
 
thanks Rams for your help. in fact, increasing viscosity ratio is decreasing turbulente dissipation rate or increasing turbulente kinetic energy for a fixed velocity inlet. can I increase vicosity ratio limit directly?


Rams June 8, 2007 05:26

Re: Moving Reference Frame
 
before going for changing increasing viscosity ratio, see whether the viscosity ratio limited in number of cells is decresing or not, if so then u need not increase the limit.

and incresing the limit will definitely effect turbulence, so it depends on u'r problem physics,

u can try out a run by increasing the viscosity ratio n check the result

lila June 8, 2007 09:05

Re: Moving Reference Frame
 
hi Rams viscosity ratio is increasing at each iteration. and as you said incresing the limit will definitely effect turbulence. I 'll try to do sensitivity analysis on turbulente parameters. thank you for your advice and help.

do you know what is the criterion convergence that I should use for momentum, k and e?



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