How to predict the transition line in CFD?

k.vimalakanthan · November 16, 2011, 14:49

Hi guys,

Could anyone please tell me how to actually predict transition in a 3D CFD simulation, especially at the geometry wall?

I'm using the SST Gamma Theta transition model to conduct my simulations, where I have the parameters of turbulent kinetic energy, intermittency and ReTheta of the flow are made available. I'm not sure if they will exist at the geometry wall due to the no slip condition.

I would like to separate the region of the laminar flow and turbulent flow, i.e. some flow variable that represent only transition or laminar or turbulent.

Have seen of the use of wall shear stress (contour) to predict transition, but is there a way to draw a definite line of the flow transition?

Any help is greatly appreciated
Thanks in advance

sail · November 16, 2011, 14:53

hi there. what i usually do when using this model is to take a look at the wall shear stress.

the transition should then be quite noticeable.

i don't understand exactely what your mena by drawing a definite line. do you mean by hand or in within the sw?

maybe an isocontour of the wall shear stress should do the trick, or changing the legend scale to plot only the values of the turbulent or laminar region, but i don't see any differences in comparing the plot as a whole.

but again, it might just be that i've not understood completely your issue.

aerospaceman · November 23, 2011, 05:00

It seems you want to run your simulation in two different regimes.

What I don't understand is if you already have your solution from your turbulence model, why do you want to redefine this point? You can just plot Cp vs x.

Depending on the software (eg Star-CCM+) you can manually specify where you want transition to occur, but this is normally not "the" way to go about it.

November 16, 2011, 14:49	How to predict the transition line in CFD?	#1
k.vimalakanthan Member Kisorthman Vimalakanthan Join Date: Apr 2011 Posts: 46 Rep Power: 15	Hi guys, Could anyone please tell me how to actually predict transition in a 3D CFD simulation, especially at the geometry wall? I'm using the SST Gamma Theta transition model to conduct my simulations, where I have the parameters of turbulent kinetic energy, intermittency and ReTheta of the flow are made available. I'm not sure if they will exist at the geometry wall due to the no slip condition. I would like to separate the region of the laminar flow and turbulent flow, i.e. some flow variable that represent only transition or laminar or turbulent. Have seen of the use of wall shear stress (contour) to predict transition, but is there a way to draw a definite line of the flow transition? Any help is greatly appreciated Thanks in advance __________________ Kisorthman Vimalakanthan Dept. of Power and Propulsion Cranfield University Email: k.vimalakanthan@gmail.com

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November 16, 2011, 14:53		#2
sail Senior Member Vieri Abolaffio Join Date: Jul 2010 Location: Always on the move. Posts: 308 Rep Power: 16	hi there. what i usually do when using this model is to take a look at the wall shear stress. the transition should then be quite noticeable. i don't understand exactely what your mena by drawing a definite line. do you mean by hand or in within the sw? maybe an isocontour of the wall shear stress should do the trick, or changing the legend scale to plot only the values of the turbulent or laminar region, but i don't see any differences in comparing the plot as a whole. but again, it might just be that i've not understood completely your issue.

November 23, 2011, 05:00		#3
aerospaceman Member Join Date: Nov 2009 Posts: 43 Rep Power: 16	It seems you want to run your simulation in two different regimes. What I don't understand is if you already have your solution from your turbulence model, why do you want to redefine this point? You can just plot Cp vs x. Depending on the software (eg Star-CCM+) you can manually specify where you want transition to occur, but this is normally not "the" way to go about it.