Simcenter STAR-CCM+ Tips and tricks for simulation of pressurized pipe

Summary

In this FAQ we try to simulate a pressurized pipe from one side and see how the pressure and density is changing in the pipe during the simulation. All other sides of the pipe are closed. We try to give you tips and tricks what would help in such a simulation.

Details

Attachments:

cylinder_6bar_end.sim.7z (44 MB)

The pipe has an initial pressure of 1 bar and from one side we try to impose a pressure of 6 bar, while the other side of the pipe is closed. In the pipe we have air as compressible ideal gas:



Although this case seems to be very simple, it turned out that this simulation is very challenging, and the boundary conditions need to be imposed carefully, to run the simulation stable.

For example using a Pressure Outlet boundary condition with 6 bar, would not run stable and the simulation would diverge quite fast. What is working here is using a Stagnation Inlet boundary condition with 6 bar as Total Pressure and 6 bar as Supersonic Static Pressure. This way we mimic best a reservoir type boundary condition. Using a Stagnation Inlet boundary condition with 6 bar as Total Pressure and 0 bar as Supersonic Static Pressure would also not work and simulation would diverge.

The boundary conditions are not the only challenges here. Due to the strong density change in the pipe (see image below), this simulation runs stable only after reducing the time step to 1e-6 s with 25 inner iterations and lowering the URF for pressure to 0.01. Please see attached test case to this article.