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-   -   Units question (http://www.cfd-online.com/Forums/openfoam-pre-processing/94180-units-question.html)

tokotico November 8, 2011 10:55

Units question
 
Hello everybody, I am using pisoFoam to run an external flow over an obstacle, I can not understand the units field in the tutorials where p has dimensions of [0 2 -2 0 0 0 0] instead of what I would expect [1 -1 -2 0 0 0 0].

can anybody point me in the right direction?


Thanks.

Bernhard November 8, 2011 11:03

The equations are solved for p/rho, so that rho only appears in the kinematic viscosity. This explains the different units.

tokotico November 8, 2011 11:08

Thanks for replying so fast Bernhard,

so the results I get for pressure need to be multiplied by rho to make them Pascals?

żdoes it make a difference if I declare units of [1 -1 -2 0 0 0 0] ?

Bernhard November 8, 2011 11:10

Yes, then they will be pascals, but be certain from the source code if it is indeed the kind of pressure you think it is.

If you change the units, the dimensions for the different terms are inconsistent. This will throw you a fatal error.


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