[Saeef]

Hello, everyone!

I'm working on the non-equilibrium condensation of supercritical CO2.

In my case setting, there are three .RGP files, including co2g, co2l and co2gl. Metastable properties filled the superheat area of co2g.rgp & co2l.rgp. As for co2gl.rgp and the saturation area of co2g.rgp & co2l.rgp, equilibrium properties are adopted.

Converged result of single phase simulation was used to initiate the field. But, after about two thousand steps, it diverged.

The solver indicated that the calculation of saturation properties beyond tables’ range, such as the saturation temperature at 8.64Mpa. Obviously, there’s no saturation data on this point.So, I’m confused.

But, if I use real gas model, such as ARK, this warning would dissapper.

[evcelica]

What are your initial conditions for Temperature and Pressure? Your temperature and pressure look like you are in the supercritical range (Pressure OR Temperature above critical), not liquid?

[ghorrocks]

This situation can come about with numerical instability. Before you look into the details of the material properties and your model you should make sure you have the basics covered:
* double precision numerics
* a good initial condition
* small time steps
* improve mesh quality

Mesh quality is a big one - if you are getting convergence issues with a prism/tet mesh then try using a very high mesh quality hex mesh. Don't trust the mesh quality guidelines in the output file, they do not apply to challenging cases like yours.

[Saeef]

Originally Posted by evcelica

What are your initial conditions for Temperature and Pressure? Your temperature and pressure look like you are in the supercritical range (Pressure OR Temperature above critical), not liquid?

Hello, evcelica

The initial temperature is indeed higher than the critical temperature. But it did not give warning if the ARK equation were applied rather than RGP files. So I don't think it caused the problem.

[Saeef]

Originally Posted by ghorrocks

This situation can come about with numerical instability. Before you look into the details of the material properties and your model you should make sure you have the basics covered:
* double precision numerics
* a good initial condition
* small time steps
* improve mesh quality

Mesh quality is a big one - if you are getting convergence issues with a prism/tet mesh then try using a very high mesh quality hex mesh. Don't trust the mesh quality guidelines in the output file, they do not apply to challenging cases like yours.

Thank you for advice. The pure hex mesh is used in the calculation.

But it still diverged.

[evcelica]

If you are supercritical do not use liquid rgp table, or phase change model. You will not have a phase change, it will always be supercritical fluid (vapor).

[LUO DAN]

Originally Posted by Saeef

Hello, everyone!

I'm working on the non-equilibrium condensation of supercritical CO2.

In my case setting, there are three .RGP files, including co2g, co2l and co2gl. Metastable properties filled the superheat area of co2g.rgp & co2l.rgp. As for co2gl.rgp and the saturation area of co2g.rgp & co2l.rgp, equilibrium properties are adopted.

Converged result of single phase simulation was used to initiate the field. But, after about two thousand steps, it diverged.

The solver indicated that the calculation of saturation properties beyond tables’ range, such as the saturation temperature at 8.64Mpa. Obviously, there’s no saturation data on this point.So, I’m confused.

But, if I use real gas model, such as ARK, this warning would dissapper.

hi,
how do you generate co2gl.rgp?CFX can not read my RGP file.

[aiyinsitan]

Have you solved the problem now? I am currently simulating the flow of subcritical CO2 in the nozzle with the same problem. My email address is 2018226210012@stu.scu.edu.cn

[aiyinsitan]

Originally Posted by LUO DAN

hi,
how do you generate co2gl.rgp?CFX can not read my RGP file.

Have you solved the problem now? I am currently simulating the flow of subcritical CO2 in the nozzle with the same problem. My email address is 2018226210012@stu.scu.edu.cn