K epsilon Model

CFD22 · July 21, 2015, 11:14

Hello,

i am working on a small projekt with star ccm+. I am using a k Epsilon model for turbulence. Ist used to estimate the reynolds stresses for high reynolds numbers. But i think there is a second one, for low reynolds numbers.

Can anyone explain me the difference between this two equations?

Standard k Epsilon model and low reynolds number model.

thank you

edoan · July 21, 2015, 13:38

The difference in the two models comes in how they treat the near wall flow. The low Re model is supposed to be used with a mesh that has a y+ value = 1. This low re model is resolving the flow all the way to the wall. The standard model is to be used with a mesh that has a y+ value of 30-300 it uses wall functions to resolve the flow near the wall. These two models can be used to model the same flow the "low Re" model does not mean its used for only low reynolds number flows, it is talking about the laminar flow near the wall. If you can search about what y+, wall functions, and boundary layer you will easily understand the difference between these two models.

CFD22 · July 21, 2015, 15:27

thank you for your answer, it helps me

July 21, 2015, 11:14	K epsilon Model	#1
CFD22 New Member Manuel Hagen Join Date: Jul 2015 Posts: 4 Rep Power: 11	Hello, i am working on a small projekt with star ccm+. I am using a k Epsilon model for turbulence. Ist used to estimate the reynolds stresses for high reynolds numbers. But i think there is a second one, for low reynolds numbers. Can anyone explain me the difference between this two equations? Standard k Epsilon model and low reynolds number model. thank you

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July 21, 2015, 13:38		#2
edoan Member Ethan Doan Join Date: Oct 2012 Location: Canada Posts: 90 Rep Power: 14	The difference in the two models comes in how they treat the near wall flow. The low Re model is supposed to be used with a mesh that has a y+ value = 1. This low re model is resolving the flow all the way to the wall. The standard model is to be used with a mesh that has a y+ value of 30-300 it uses wall functions to resolve the flow near the wall. These two models can be used to model the same flow the "low Re" model does not mean its used for only low reynolds number flows, it is talking about the laminar flow near the wall. If you can search about what y+, wall functions, and boundary layer you will easily understand the difference between these two models.

July 21, 2015, 15:27		#3
CFD22 New Member Manuel Hagen Join Date: Jul 2015 Posts: 4 Rep Power: 11	thank you for your answer, it helps me