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dfytanid September 16, 2009 08:15

What does “Mean Wall Shear Stress” mean?
I am running an unsteady simulation and I have a question about unsteady wall statistics.

Having already activated the data sampling from the iteration menu I use the Unsteady wall statistics and more specificly the Mean wall shear stress option from Display/Contours../ .
And now the question is: How does fluent calculate this “Mean” values??
Is it the mean from the magnitudes of the shear vectors or
the magnitude of the mean shear vector?? (Please see the following equations)

Mean WSS=\frac{\sum|\vec{WSS}|_{t}}{number of time steps} or

Mean WSS=\frac{|\sum\vec{WSS}_{t}|}{number of time steps}

In some cases it is the same but in my case I have a variable velocity inlet (with positive and negative values) and thus the Shear Vector change direction.

Thank you for your answers,

amindari October 14, 2016 09:19

HEY dim
have you found the answer?

dfytanid October 14, 2016 13:16


Originally Posted by amindari (Post 621524)
HEY dim
have you found the answer?

Yeap. What Fluent calculates is the average wss magnitude.
The magnitude of the average wall shear stress vector has to be calculated either using a UDF or in a post-processing tool(.e.g Post-CFD, tecplot etc).

vasava October 17, 2016 01:05

Are you calculating OSI? If so, it would be interesting to know your approach.

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