SimScale CAE Forum

Pressure Drop Across Post Combustion Chamber

Hi all,

I am trying to simulate a pressure drop across a post combustion chamber. The fluid material moving through is air at very lower speeds and pressure, so we can assume it is incompressible.

I am having problems with a diverging velocity result.

The first run was successful and the conditions I used to set it up were high (just to test the simulation). I used a pressure inlet and a volumetric flow outlet. When changing the boundary conditions on consequent runs to a more realistic scenario, the simulation always fails and returns an error of diverging velocity results at a point near the inlet.
Failed run:


Successful run:

Here is the project link: https://www.simscale.com/workbench/?pid=3946876803260285172&mi=run%3A16%2Csimulation%3A10&mt=SIMULATION_RUN

As you can see first run is successful and others fail, can anyone please asssist?

Kind Regards

Hi, please have a look on the definition of the pressure inlet boundary.
It’s currently set to a fixed value of -10 Pa which leads to very high inlet velocity. Changing it to Total pressure should fix that issue.

Also I calculated the outlet Velocity of your Volumetric flow outlet and i calculated for 26m³/s and a face area of 0.076m²that the velocity will be around 340 m/s. This is velocity is equal to Mach 1 so you cannot assume incompressible flow. ( up to Mach 0.3).

I hope that helps with your issues.

Best regards Sebastian