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wall shear stress formulation

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Old   June 27, 2011, 12:42
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Rakesh
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Dear All!

what is the correct equation for finding wall shear stress in X and Y direction in ANSYS FLUENT FOR WRITING UDF?

I assume that for X direction wall shear stress=mu*du/dy and for Y DIRECTION =mu*dv/dx
.please confirm.
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Old   June 28, 2011, 07:51
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Quote:
Originally Posted by rakadit View Post
Dear All!

what is the correct equation for finding wall shear stress in X and Y direction in ANSYS FLUENT FOR WRITING UDF?

I assume that for X direction wall shear stress=mu*du/dy and for Y DIRECTION =mu*dv/dx
.please confirm.
Dear Rakesh,
Unfortunately, there is a big bug in computing wall shear stress in FLUENT. To write a UDF for this purpose, use normal vectors of each element to project tensor elements.
PS:
T=2.0*mu*D ; D=0.5*(del(v)+trans(del(v)))
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Old   July 7, 2011, 01:40
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Dear Mr. Amir,

Thanks for your suggestion.I tried this concept for writing udf for wall shear but I could not implement del(v) and trans( v) functions.

Actually in the previous UDF , which you had corrected for wall shear, results are coming but I am not getting boundary layer velocity gradients.I am getting velocity gradients just in the flow direction .

Now ,I have written new UDF with suggestions from people on net,where dudy MACRO is replaced by f-u(f,t)-c-u(c,t) etc. concept.I have posted this UDF on this site. I am getting some problem with it.

please help to rectify the problem. My aim is to model wall shear in a way that ,instead of no slip condition,non-zero velocity is obtained in the transverse direction(prep. to flow).

Thanks for all your help.

Rakesh
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Old   August 17, 2011, 12:48
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Quote:
Originally Posted by Amir View Post
Dear Rakesh,
Unfortunately, there is a big bug in computing wall shear stress in FLUENT. To write a UDF for this purpose, use normal vectors of each element to project tensor elements.
PS:
T=2.0*mu*D ; D=0.5*(del(v)+trans(del(v)))
salam amir jan
agha man ye moshkele kheili bozorg ba hamin ghaziyeye wall normal and shear stress daram mitunid komakam konid plz?
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