units in OpenFOAM
I am getting confused about the units used in OpenFOAM for some parameters, especially p and phi.
1. p has to be given with units m2/s2 in simpleFoam (which actually are the units of p/rho) but with the usual units kg/m/s2 in reactingFoam for example.
I´m pretty sure this has something to do with incompressibility but I am not quite sure and I don´t get why it is programmed this way.
2. phi is rho.U (e.g. User Guide 1.7.1 p.115 or 2.0.0 p.118), right? It thus should have units kg/m2/s but has units m3/s in the time step folders. why is that so?
This question might result from a bad understanding of what phi is. Complementary information about it too would be appreciated.
Thanks for your help.
1. With constant density, you can divide the entire equation with rho and you will end up with a modified pressure, and thus the "uncommon" units.
2. phi is U * Sf (velocity times surface area) in all the solvers I worked with.
Thanks for your answer.
I´m a bit confused though. As I mentioned, phi is defined as rho * U in the User Guide (p.115 or p.118). Does that mean the definition varies depending on the situation studied or the solver used?
in simpleFoam you assume constant density.
phi = rho*U*Sf [kg/s] in the convective term
as rho is constant you can divide the whole equation by rho as akidess posted before. And so you get
phi = U*Sf [m³/s]
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