Turbulence Boundary Conditions

f.capaldi · October 15, 2015, 11:19

I am conducting a study into turbulent flow around imperfect cylinders. I am relatively new to turbulence modelling.
I have a cylinder placed in a rectangular domain and I am simulating and external flow at Re 20000 using the Spalart Almaras model. Cylinder diamter is 0.01m.
Does anyone have any suggestions for how to calculate or what values to use for Turbulence Intensity, Turbulence Length Scale and Turbulence Velocity Scale?

Thanks

LuckyTran · October 15, 2015, 16:53

If the oncoming flow is quiescent then it wouldn't have any turbulence. So your intensity and length scale should be 0. The turbulence is generated by your cylinder.

If the oncoming flow is not quiescent then you need to consider where that flow is coming from and what is the source of the turbulence? Maybe there is a flagpole upstream? A boundary layer from the earth or your wind tunnel? A flock of birds? An elephant. etc.

f.capaldi · October 18, 2015, 15:03

Ah I see, I thought it may be 0 but then the cylinder in this example would be modelling a bridge cable in free stream flow. I imagine there would be some degree of turbulence in any airflow due to interactions not directly involving the bridge (combing airflows upstream, land or water)

October 15, 2015, 11:19	Turbulence Boundary Conditions	#1
f.capaldi New Member Francis Capaldi Join Date: Oct 2015 Posts: 3 Rep Power: 11	I am conducting a study into turbulent flow around imperfect cylinders. I am relatively new to turbulence modelling. I have a cylinder placed in a rectangular domain and I am simulating and external flow at Re 20000 using the Spalart Almaras model. Cylinder diamter is 0.01m. Does anyone have any suggestions for how to calculate or what values to use for Turbulence Intensity, Turbulence Length Scale and Turbulence Velocity Scale? Thanks

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October 15, 2015, 16:53		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,754 Rep Power: 66	If the oncoming flow is quiescent then it wouldn't have any turbulence. So your intensity and length scale should be 0. The turbulence is generated by your cylinder. If the oncoming flow is not quiescent then you need to consider where that flow is coming from and what is the source of the turbulence? Maybe there is a flagpole upstream? A boundary layer from the earth or your wind tunnel? A flock of birds? An elephant. etc.

October 18, 2015, 15:03		#3
f.capaldi New Member Francis Capaldi Join Date: Oct 2015 Posts: 3 Rep Power: 11	Ah I see, I thought it may be 0 but then the cylinder in this example would be modelling a bridge cable in free stream flow. I imagine there would be some degree of turbulence in any airflow due to interactions not directly involving the bridge (combing airflows upstream, land or water)