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-   -   Wall shear stress (http://www.cfd-online.com/Forums/openfoam-solving/59133-wall-shear-stress.html)

andrewburns February 12, 2008 18:16

Hello, I'm trying to figure ou
 
Hello, I'm trying to figure out the dimensions of openFoam's wall shear stress. I'm trying to compare the same mesh run for the same conditions in both fluent and openFoam, however when I use wallShearStress to find the stress on the openFoam case I get numbers that are much different to those from fluent.

I know fluent calculates wall shear stress in pascals, however when I look at the dimensions in the shear stress file generated by openFoam I see this:

[0 2 -2 0 0 0 0]

Wouldn't this mean the units for shear stress in openFoam are m^2/s^2 ? I don't understand how this can be converted to pascals for comparison purposes.

For an idea of the differences I'm talking about, fluent reports the maximum shear stress as 14 pascals, while openFoam reports it as 53.6.

dmoroian February 13, 2008 02:44

For an incompressible flow, al
 
For an incompressible flow, all the equations are divided with density. If you divide [Pa] with r, it should go like this:
Pa/r = N/m2/kg/m3 = kg*m/s2/m2/kg/m3 = m2/s2

I hope this is helpful!
Dragos

andrewburns February 13, 2008 17:40

Thanks that's perfect. I thoug
 
Thanks that's perfect. I thought it would be something like that but I wasn't able to work out if it made sense dimensionally.


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