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June 12, 2012, 09:03 |
Physic of the field function
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#1 |
Member
David L
Join Date: May 2012
Posts: 43
Rep Power: 14 |
Hi guys
I look for exactly that do a field function of Star ccm+ for calculating WALL Y+, I want to know what? the reason? for using this field fucntion from Star ccm+ ... maybe you could said where I find the definition of the WALL Y+, because I do not find in the help it. |
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June 12, 2012, 14:18 |
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#2 |
Member
David L
Join Date: May 2012
Posts: 43
Rep Power: 14 |
WALL Y+ is value*u*y/v *where*
u**is the reference velocity,* y is the normal distance from the centroid to the wall in wall-adjacent cells* v***is the kinematic viscosity. |
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June 13, 2012, 08:52 |
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#3 |
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Ryan Coe
Join Date: Jun 2010
Location: Albuquerque, NM
Posts: 98
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If I understand your question correctly (not sure if I do):
In general, y+ is used a measure of distance in which parts of the boundary layer can be generally defined (see http://en.wikipedia.org/wiki/Law_of_the_wall). The wall y+ field function gives the y+ value at the center of the cell closest to a wall. It is a useful measure of how well you mesh is resolving the boundary layer (lower number = better resolution). Hopefully this helps.
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Ryan |
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June 14, 2012, 18:59 |
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#4 |
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David L
Join Date: May 2012
Posts: 43
Rep Power: 14 |
thanks so much
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June 15, 2012, 15:58 |
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#5 |
Senior Member
Join Date: Oct 2009
Location: Germany
Posts: 636
Rep Power: 21 |
I'm sorry Ryan, I have to partly disagree.
A lower number does not automatically mean you better resolve the boundary layer. That's also dependent on the number of layers. The wall Y+ just let you know if your first cell center is within the viscous layer or in the logarithmic range of the log wall law (or anywhere in between). A low Y+ doesn't give any advantage when you don't have enough cells to resolve the boundary layer.
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