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NS-Equations an p-dimension

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Old   June 14, 2014, 12:41
Default NS-Equations an p-dimension
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Olivia Nalen
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Hello dear foamers,

Does someone know, why is the dimension of pressure p [0 2 -2 ...]? That means, the pressure is actually not pressure, but pressure/density.

And that's why should be the NS-equations defined not for pressure, but for pressure*density.

Is this correct too?

Kind regards, Olivia
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Old   June 14, 2014, 12:55
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Alexey Matveichev
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Hi,

these units are used only for incompressible N-S equations (as in this case you can just divide equations by density), if you take a look at ICs/BCs in compressible solvers examples, there units of pressure are Pa.
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Old   June 14, 2014, 14:04
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Olivia Nalen
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Hello Alexey,

thanks for an fast answer

You said, I can divide equations by density, but I wonder, whether I had to? Or maybe I just can say that my density (air) = 1 and not worry about that?



Kind regards, Olivia
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Old   June 14, 2014, 15:13
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Well,

Incompressible NS solvers in OpenFOAM are already implemented for equations that are divided by density (except multiphase solvers).

If you'd like to implement your own solver, no you don't have to divide equations.

If you'd like to use Pa for pressure, you have to correct units for other properties of the system, like viscosity (it'll become dynamic instead of kinematic, at this point you also need to correct turbulence model as for incompressible solvers turbulent viscosity is kinematic). These are the ones that come to mind, guess there can be other properties that are introduced through fvOptions mechanism.
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Old   June 14, 2014, 18:19
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Olivia Nalen
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Thanks a lot again,
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