Pb in conv. k-e 3D Help

fluser · October 30, 2009, 05:27

Hello,
I am running a 3d simulation using the standard K-E model.

after 10 iterations "sliding mesh simulation" (in steady state flow) values of k & epsilon are diverging. I have the message: "Turbulent viscosity limited to viscosity ratio of 1e5 in cells".
I used pressure based solver.

Can anyone help with this please? Thanks.

CFD_4 · October 30, 2009, 05:28

pl. check mesh quality.

fluser · October 30, 2009, 05:44

I do grid--check, everything is good!

fluser · October 30, 2009, 06:18

and if I make simulation in laminar flow, solution converge!

tez · October 30, 2009, 15:51

Try with very small under-relaxation numbers and gradually increase them to default values. That might help.

fluser · November 2, 2009, 06:16

Hi Tez,
I divided UR factors by 100, results are better . but there are fluctuations of the epsilon parameter. After 100 iterations the residuals of k and e parameters are about 5.e-2.
tell me plz. how to increase gradually these parameters? by stopping and restart calculation and increasing URP without initializing?

greeneye · November 3, 2009, 06:42

I think it is better to give a inviscid solution and then set it as a intial condition for turbulent solution.another way is to set the "turbulent insity" and "turbulent viscousity ratio" to 1 at velocity inlet.

fluser · November 4, 2009, 05:26

Hi greeneye,
I apply your second proposition but k & epsilon residuals remind at too high values (about 1.e-1).
I have a simple question for you: how to use a solution as an initial condition in Fluent?
by iterating without initilize solution?
thanks

October 30, 2009, 05:27	Pb in conv. k-e 3D Help	#1
fluser New Member Mines Join Date: Oct 2009 Posts: 5 Rep Power: 16	Hello, I am running a 3d simulation using the standard K-E model. after 10 iterations "sliding mesh simulation" (in steady state flow) values of k & epsilon are diverging. I have the message: "Turbulent viscosity limited to viscosity ratio of 1e5 in cells". I used pressure based solver. Can anyone help with this please? Thanks.

October 30, 2009, 05:28	mesh	#2
CFD_4 New Member wayusen Join Date: Oct 2009 Location: Pune Posts: 6 Rep Power: 16	pl. check mesh quality.

November 3, 2009, 06:42	hello	#7
greeneye New Member reza Join Date: Nov 2009 Posts: 5 Rep Power: 16	I think it is better to give a inviscid solution and then set it as a intial condition for turbulent solution.another way is to set the "turbulent insity" and "turbulent viscousity ratio" to 1 at velocity inlet.

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October 30, 2009, 05:44		#3
fluser New Member Mines Join Date: Oct 2009 Posts: 5 Rep Power: 16	I do grid--check, everything is good!

October 30, 2009, 06:18		#4
fluser New Member Mines Join Date: Oct 2009 Posts: 5 Rep Power: 16	and if I make simulation in laminar flow, solution converge!

October 30, 2009, 15:51		#5
tez New Member Tez Join Date: Oct 2009 Posts: 12 Rep Power: 16	Try with very small under-relaxation numbers and gradually increase them to default values. That might help.

November 2, 2009, 06:16		#6
fluser New Member Mines Join Date: Oct 2009 Posts: 5 Rep Power: 16	Hi Tez, I divided UR factors by 100, results are better . but there are fluctuations of the epsilon parameter. After 100 iterations the residuals of k and e parameters are about 5.e-2. tell me plz. how to increase gradually these parameters? by stopping and restart calculation and increasing URP without initializing?

November 4, 2009, 05:26		#8
fluser New Member Mines Join Date: Oct 2009 Posts: 5 Rep Power: 16	Hi greeneye, I apply your second proposition but k & epsilon residuals remind at too high values (about 1.e-1). I have a simple question for you: how to use a solution as an initial condition in Fluent? by iterating without initilize solution? thanks