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March 16, 2013, 22:11 
What is the meaning of stress free boundary condition?

#1 
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Govindaraju
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Dear all
I have come across stress free boundary condition at the outlet in a pressure drop analysis in many journals ( Transient analysis). I have confused with 0 Pa setup at the outlet with stress free boundary condition. for stress free boundary condition, I assume that the initial condition pressure setup and outlet boundary condition must be the same. Please correct me if I am wrong. Thank you Regards Govind 

March 18, 2013, 11:26 

#2 
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OJ
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From what I understand, the stressfree boundary condition must be "shearstress free" boundary condition which can be symmetry or free slip wall
Analogically, since three is no change in velocity perpendicular to the boundary (unlike wall where we have significant velocity gradient), the shear stress value should be zero/negligible. Though, you may want to confirm this with a bit of literature search. OJ 

March 19, 2013, 02:57 

#3  
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Govindaraju
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Quote:
Thank you for your reply so, stress free boundary condition doesn't mean that outlet pressure equals to zero . Am I correct? I know the symmetry boundary condition where all the normal component should be zero. consider a pipe , how do you apply symmetry boundary condition at the outlet face? if so what does it mean? when we apply free slip boundary condition at the outlet face? Thank you Regards Govind Last edited by kmgraju; March 19, 2013 at 03:21. 

March 19, 2013, 05:31 

#4 
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Glenn Horrocks
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This question has been asked a few times on the forum. Do a search of the forum for more details. I recall the stress free BC is zero normal gradient at the outlet. CFX does not implement the outlet boundary exactly this way, read the documentation for what it does do. And implementing a zero stress BC is going to be difficult, and frankly why bother when the built in outlet boundary is better in many ways.


March 19, 2013, 05:41 

#5  
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OJ
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Quote:
Ref: Houseman, G. A. "Boundary Conditions and Efficient Solution Algorithms For the Potential Function Formulation of the 3‐D Viscous Flow Equations." Geophysical Journal International 100.1 (1990): 3338. Quote:
Quote:
OJ 

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