Learning Forum

[Gilles Butikofer]

Hello there,

I'm having a troubles 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). At the beginning of the experiment, there's 1 atm of air inside the volume.

The decrease in pressure I get is way less than what's observed with the experiments and the analytical estimation. 
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My simulation is a watertight geometry with only one outlet.

I use the Density based solver. 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. (I tried other real gasses models as well, and tried many viscous models)

My mesh has a good quality, I kept the number of nodes around 1M beceause it's taking too long otherwise. (even as I'm computing on a Calculator)

Transient simulation, time steps of 1e-4 s. The Solution is converging properly, with 20 it/time step at the beginning and then reducing it to 3. 

From experimental and analytical pov, we know that we should observe a drop in pressure of about 5800 Pa in the volume after 10 seconds. However, The simulation only gives me a 10 Pa pressure drop. I'm attaching images here : https://www.swisstransfer.com/d/d29e23d6-0a70-48e6-923d-76c0e16e8a54 as i can't attach them down here, idk why. 

What am I missing ? 
Thanks for your time reading me

[Rob]

Staff aren't permitted to open files or links so you'l need to post images here.  

If you monitor domain mass (volume report) as well as pressure does that make sense?