NS-Equations an p-dimension
 

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

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.

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

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.

Thanks a lot again, :)