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gradient wall shear stress

Posted Jul 4, 2011, 12:49 p.m. EDT Computational Fluid Dynamics (CFD) Version 4.1 4 Replies

Guillermo Vilaplana
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Hi all,

I am computing the flow into a curved pipe, and I would like to plot the spatial gradient of wall shear stress.
-The command dtang(WSS, x) gives an error (could not evaluate the expression)
-The command d(WSS,x) gives 0....

Exporting to Matlab seems to be a complicated solution since the points on the surface of the pipe are exported in a list and therefore the calculus of the gradient is tricky.


Any ideas??

Thank you!
Guillermo
4 Replies Last Post May 11, 2012, 1:48 p.m. EDT
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Hello Guillermo Vilaplana

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Sirisha Govindaraju
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Posted: 1 decade ago Feb 19, 2012, 10:35 p.m. EST
Hi,

I am wondering if anybody knows how to compute wall shear stress gradient using COMSOL. I tried but it is not working.

Thanks,
Sirisha
Hi, I am wondering if anybody knows how to compute wall shear stress gradient using COMSOL. I tried but it is not working. Thanks, Sirisha
Wiktor Stenström
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Posted: 1 decade ago Feb 20, 2012, 4:51 a.m. EST
Hi,

This is the way I go about to obtain the WSS and its gradient:

-First I create WSS as a variable along the boundary of interest.
Eg. WSS = sqrt(spf.K_stressz^2 + spf.K_stressr^2)
This is for a 2D axisymmetric case where only the r and z component of the viscous stress tensor is included.
- Then the GWSS is defined as:
GWSS = sqrt(d(spf.K_stressz,z)^2 + d(spf.K_stressr,r)^2)

This returns the magnitude of the GWSS at a point (along the geometry) but in the same manner the components in z,r-directions could be obtained.
Hi, This is the way I go about to obtain the WSS and its gradient: -First I create WSS as a variable along the boundary of interest. Eg. WSS = sqrt(spf.K_stressz^2 + spf.K_stressr^2) This is for a 2D axisymmetric case where only the r and z component of the viscous stress tensor is included. - Then the GWSS is defined as: GWSS = sqrt(d(spf.K_stressz,z)^2 + d(spf.K_stressr,r)^2) This returns the magnitude of the GWSS at a point (along the geometry) but in the same manner the components in z,r-directions could be obtained.
Andrew Tan
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Posted: 1 decade ago Apr 3, 2012, 5:05 a.m. EDT

Hi,

This is the way I go about to obtain the WSS and its gradient:

-First I create WSS as a variable along the boundary of interest.
Eg. WSS = sqrt(spf.K_stressz^2 + spf.K_stressr^2)
This is for a 2D axisymmetric case where only the r and z component of the viscous stress tensor is included.
- Then the GWSS is defined as:
GWSS = sqrt(d(spf.K_stressz,z)^2 + d(spf.K_stressr,r)^2)

This returns the magnitude of the GWSS at a point (along the geometry) but in the same manner the components in z,r-directions could be obtained.


Hi, Wiktor Stenström,

May i know why you dont use spf.K_stressphi component?
i thought the phi is sqrt(r^2+z^2), am i right?
[QUOTE] Hi, This is the way I go about to obtain the WSS and its gradient: -First I create WSS as a variable along the boundary of interest. Eg. WSS = sqrt(spf.K_stressz^2 + spf.K_stressr^2) This is for a 2D axisymmetric case where only the r and z component of the viscous stress tensor is included. - Then the GWSS is defined as: GWSS = sqrt(d(spf.K_stressz,z)^2 + d(spf.K_stressr,r)^2) This returns the magnitude of the GWSS at a point (along the geometry) but in the same manner the components in z,r-directions could be obtained. [/QUOTE] Hi, Wiktor Stenström, May i know why you dont use spf.K_stressphi component? i thought the phi is sqrt(r^2+z^2), am i right?
Sirisha Govindaraju
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Posted: 1 decade ago May 11, 2012, 1:48 p.m. EDT
How to compute WSSG for a 3D geometry?
Textbook definitions talk about using the squareroot of the sum of the squares of the shear stress in the local tangential and local normal directions. How do we compute or find out the local tangential and local normal directions?

Thanks,
Sirisha
How to compute WSSG for a 3D geometry? Textbook definitions talk about using the squareroot of the sum of the squares of the shear stress in the local tangential and local normal directions. How do we compute or find out the local tangential and local normal directions? Thanks, Sirisha

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