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calculation of shear stress

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Old   June 10, 2018, 05:27
Default calculation of shear stress
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A. Min
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Hi

I want to use shear stress tensor at the middle of a code.
Which one is correct and why?

Code:
tau = mu * dev(twoSymm(fvc::grad(U)));
Or

Code:
tau = mu * twoSymm(fvc::grad(U));
I saw in forces.C code that deviatoric component of stress tensor (dev(...)) is used, do you know why?


Regards
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Old   June 11, 2018, 03:15
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Quote:
Originally Posted by alimea View Post
Hi

I want to use shear stress tensor at the middle of a code.
Which one is correct and why?

Code:
tau = mu * dev(twoSymm(fvc::grad(U)));
Or

Code:
tau = mu * twoSymm(fvc::grad(U));
I saw in forces.C code that deviatoric component of stress tensor (dev(...)) is used, do you know why?


Regards
Is your flow compressible? One is a generalization!
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Old   June 11, 2018, 03:24
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Quote:
Originally Posted by Santiago View Post
Is your flow compressible? One is a generalization!
No, that is incompresible
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Old   June 11, 2018, 04:43
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Quote:
Originally Posted by alimea View Post
No, that is incompresible
Again, mathematically, the two eqns are equivalent. Numerically, they're not, and are higly dependent on the Pressure Poisson residuals.
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