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PengRobinson floating point exception

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Old   May 10, 2020, 12:43
Post PengRobinson floating point exception
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Hello CFDler,

i am working on a simulation with fluid CO2 through a diffusor at 60 bar and roomtemepratur. The fluid should pressure driven exit the nozzle.

I started my first simulation with the Equation of state perfectGas which worked. Now i changed the EOS to PengRobinsonGas and now i get a "floating point exception" (division through zero) after a few iterations.

In this link you can find my case with the log File:

https://drive.google.com/open?id=1wv...zqL9c6CEc9YcxU

I already tried to change the Boundarys, the numeric and my mesh without any oblique lines but nothing worked.

Any suggestions?

Greatings

Daniel
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Old   May 11, 2020, 05:34
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In most cases, when using real equations of state, the CFD user is not aware that in some areas the setup surpasses the physical limits of the EOS.
I would suggest, to modify your thermodynamic states and approach the initial condition in stages, e.g. reduce your pressure to 1 bar at 293.15 K temperature.

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Old   May 11, 2020, 05:40
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Quote:
Originally Posted by Eifoehn4 View Post
In most cases, when using real equations of state, the CFD user is not aware that in some areas the setup surpasses the physical limits of the EOS.
I would suggest, to modify your thermodynamic states and approach the initial condition in stages, e.g. reduce your pressure to 1 bar at 293.15 K temperature.

Regards
Thank you. When i change my pressure settings to 2bar the simulations starts and runs. With 8 bar i get the same error but it runs longer.

So you're recommending to increase the pressure on the fly?
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Old   May 11, 2020, 06:58
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Not exactly, i mean that you should be aware if your underlying problem may produce non-physical conditions for you geometrical setup.

Independantly of this, a ramping of the boundary or initial conditions is no bad choice.

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Old   May 11, 2020, 07:27
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Quote:
Originally Posted by Eifoehn4 View Post
Not exactly, i mean that you should be aware if your underlying problem may produce non-physical conditions for you geometrical setup.

Independantly of this, a ramping of the boundary or initial conditions is no bad choice.

Regards
I just tried to ramp my pressure, but for that i had to change the bcs at the inlet. With the new BCs the simulations starts, but doesnt reach the first point i had defined with "table". It ended with the same Error.
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