initial conditions

pinfan143 · July 11, 2012, 04:52

Hello every masters
I have one question , could you help me?
I have no idea about turbulence specification in the menu of initial conditions. it has three methods can be chose in star ccm+: k+epsilon, intensity+length scale and intensity +viscosity ratio.
i don't know the difference between them.
my case is a steady and constant density case, does it mean i can choose any method, the result will not be affected by the method which i chose. the only thing affected by the method is convergence rate, is it?

flotus1 · July 11, 2012, 05:47

Right you are

The choice of the initial conditions should only affect the speed of convergence.
Yet if the initial guess is totally wrong, the calculation might not converge at all.

The fact that there are 3 different options to choose from for the initial conditions of the k-epsilon model is just for your convenience.
k, epsilon, intensity, length scale and viscosity ratio can be calculated one from another.

More important than the initial guess are the turbulence specifications at the inlet.

siara817 · July 12, 2012, 09:51

which one these properties do you know for your case. Do you know for example, what is viscosity ratio for your case? It depends on your case study, what do you want to simulate? according to that you need to search for some literature. I think you can find some hint about the number you need for, for example, turbulent intensity in some literature.

July 11, 2012, 04:52	initial conditions	#1
pinfan143 New Member Aaron Gao Join Date: Jun 2012 Posts: 3 Rep Power: 13	Hello every masters I have one question , could you help me? I have no idea about turbulence specification in the menu of initial conditions. it has three methods can be chose in star ccm+: k+epsilon, intensity+length scale and intensity +viscosity ratio. i don't know the difference between them. my case is a steady and constant density case, does it mean i can choose any method, the result will not be affected by the method which i chose. the only thing affected by the method is convergence rate, is it?

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July 11, 2012, 05:47		#2
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	Right you are The choice of the initial conditions should only affect the speed of convergence. Yet if the initial guess is totally wrong, the calculation might not converge at all. The fact that there are 3 different options to choose from for the initial conditions of the k-epsilon model is just for your convenience. k, epsilon, intensity, length scale and viscosity ratio can be calculated one from another. More important than the initial guess are the turbulence specifications at the inlet.

July 12, 2012, 09:51		#3
siara817 Senior Member siamak rahimi ardkapan Join Date: Jul 2010 Location: Copenhagen, Denmark Posts: 220 Rep Power: 17	which one these properties do you know for your case. Do you know for example, what is viscosity ratio for your case? It depends on your case study, what do you want to simulate? according to that you need to search for some literature. I think you can find some hint about the number you need for, for example, turbulent intensity in some literature.