[GILLL]

Hello there,

I'm having a few issues with my simulation. I want to simulate the behaviour pressure over time of a parallelepiped vessel attached to a vacuum pump (which is just described by a mass flow outlet on the vessel). So at the beginning of the experiment, there's 1 atm of air inside the volume.

My simulation is a watertight geometry with only one outlet.

I use the Density based solver, as the pressure based solver is for incompressible gasses. (pressure based solver gives floating point exception anyways)

The fluid is air from the material fluid list, and I changed "Density" parameter from constant to ideal gas, so density can vary, accordingly to P and T. Or at least, that's my expectation.

However, even after multiple time steps, my monitoring points of the pressure on the face of the inner volume, and the pressures I see on the cfd post are 0 Pa on most of the volume, except where the gas flows quicker close to the outlet where I see negative pressure values, due to the velocity..
I can also see that the density of the air doesn't changes at all from its initial value.

What am I missing ?
Thanks for your time reading me

It seems that "Pressure" is a relative value, so 0 Pa is like having 1 atmosphere, right ? and it is not a total pressure since I can observe a lower pressure where there's higher velocities.

[GILLL]

I was using 2 seconds time steps, apparently it's too much. I should be using 1e-4 to 1e-3 with less iterations per ts

I'll update if that's my issue

--
Edit: well it helps a little bit, but I'm getting a 10 Pa pressure drop after 10s, with time steps of 1e-4s. from the experiments and my hand calculations, I should expect a 5800 Pa pressure drop. I tried to change the properties of the air, especially the density. I tried also other turbulent models, saw a few changes but basically it's the same outcome.

I read something about floating operating pressure, but im not able to activate it in my operating parameters, I can only give a constant operating pressure or an expression. should I make an expression for this ?