Transition point prediction in Star CCM

rishabhk28 · April 22, 2018, 10:34

I'm using Star CCM+ 12.02 for stimulating incompressible flow over an axisymmetric body.

i need help regarding the following:
how to know the transition point over the body
and How can I see which part of the body is experiencing a laminar flow

please LMK if any additional information is needed. thank you so much for your time!

fluid23 · April 23, 2018, 09:52

Technically speaking, a transition point is a numerical construct that you impose on an analysis. Natural transition is not an instantaneous phenomenon but rather a process that happens over a region. You can determine the approximate location by looking at shear stress along the surface and when it jumps from low-to-high you can assume that the flow has transitioned. However; the when, where and how of this transition is greatly influenced by your model and physics setup. You should try to work some validation cases first so you understand how to get acceptable results that can be verified before trying to model something more complex.

LuckyTran · April 30, 2018, 22:59

The wall shear stress check is a good one I think.

Try plotting the ratio of the eddy viscosity to the effective viscosity (laminar + turbulent viscosity). When the ratio is very low then you're laminar, when it's positive then you're more turbulent.

If you're using a transitional model, there is an intermittency variable which tells you how much time the flow spends in laminar vs turbulent state. 0 for always laminar, 1 for always turbulent and between 0 and 1 is transitional.

April 22, 2018, 10:34	Transition point prediction in Star CCM	#1
rishabhk28 New Member Rishabh Kumar Join Date: Sep 2017 Posts: 9 Rep Power: 8	I'm using Star CCM+ 12.02 for stimulating incompressible flow over an axisymmetric body. i need help regarding the following: how to know the transition point over the body and How can I see which part of the body is experiencing a laminar flow please LMK if any additional information is needed. thank you so much for your time!

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April 23, 2018, 09:52		#2
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	Technically speaking, a transition point is a numerical construct that you impose on an analysis. Natural transition is not an instantaneous phenomenon but rather a process that happens over a region. You can determine the approximate location by looking at shear stress along the surface and when it jumps from low-to-high you can assume that the flow has transitioned. However; the when, where and how of this transition is greatly influenced by your model and physics setup. You should try to work some validation cases first so you understand how to get acceptable results that can be verified before trying to model something more complex.

April 30, 2018, 22:59		#3
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 66	The wall shear stress check is a good one I think. Try plotting the ratio of the eddy viscosity to the effective viscosity (laminar + turbulent viscosity). When the ratio is very low then you're laminar, when it's positive then you're more turbulent. If you're using a transitional model, there is an intermittency variable which tells you how much time the flow spends in laminar vs turbulent state. 0 for always laminar, 1 for always turbulent and between 0 and 1 is transitional.