[namgnirps]

Hello All,


I want to simulate the following transient system:

Fluid is flowing through a pipe and an orifice into a closed chamber. The model is rotational symmetrical, the pipe orifice and a part of the chamber is filled by liquid, the rest of the chmber with gas. I built a 2.5d model of the system with transient inlet velocity as boundary condition. The process is fast: total simulated time: t=0.1s, Re_Inlet: ca. 12000.
Now I am struggeling with the following problem:



1. Simulation Error:

If I model the gas as ideal gas, I get a stack over flow error after t=0.025s (22 timesteps). I used adaptive time steps. The last timestep is T=0.0001s, which is the minimum allowed timstep. Double precision is on.

If I use constant property gas, the simulation runs fine with a fixed timestep of T=0.005s.
Do i need to reduce the minimum timestep further? Or the the problem somewhere else in the model?


2. For the model with constant property gas:

The pressure of the gas is not increasing over time although fluid is flowing into the closed system. I guess this is the effect of a constant property gas, right? Thus, will be solved, if the ideal gas model is running...

Furthermore, the volume of the gas is not reducing proportionally to the mass flow of fluid entering the closed model. Is this also an effect of the constant property gas model?


Thank you for your support in advance!


BR,
Namgnirps