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High pressure nitrogen discharge simulation in Fluent

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Old   October 2, 2016, 17:54
Default High pressure nitrogen discharge simulation in Fluent
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Sorry to interrupt people, I am trying to simulate in Fluent a high pressure discharge of a long and thin tube (41 m long 5 mm diameter) filled with nitrogen at an initial pressure of 80 bara. The discharge is done against atmospheric conditions and the goal is to obtain the discharge times of the tube at different intial pressures.
Basically my grid is a 2D axisymmetric grid made up of a thin section which constitutes the slender tube and a a thicker section that constitutes the discharge area.
So far I have been able to run the simulation for 0.05 seg (simulation time) and captured properly the Mach disk at the outlet of the tube as well as the propagation of the expansion wave in the initial stages of the discharge.
However, I have encountered a few issues, being these:

1 - The simulation takes a lot of time to get to a result.
2 - The pressure jump that follows the initial expansion wave across the tube seems to dissipate as it propagates along the tube.

Do you have any suggestions regarding this issues?

I have tried using an adaptive time-stepping schema to get to results faster though it's quite constrained by the Courant number and although it speeds up the solution, it's still really slow. I have also implemented a Second Order Upwind schema for the convective term to avoid numerical diffusion but it imposes a bigger burden on my machine.

Thank you in advance for your time.
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