Explanation of waterAirflatInterface2d example

[CWhalley_1]

Hi all,

I have been looking into the newly added multi component example, waterAirflatInterface2d with the goal to modify a copy to simulate a liquid being injected into an air cross flow.
In trying to do this I have run into a couple of problems, the first main problem being that no matter what I have tried so far the first step always returns as an error, giving ‘Not a Number’. Whilst trying to identify what is causing this I have been trying to understand what each of the variables are, however I am a bit confused about some of them. I believe I understand most of them however if someone could please explain what T_c, p_c, g_I, and g_II are that would be much appreciated.

The second main problem has been that I have not been able to apply inlets and an outlet to the system. I have so far tried using
‘setInterpolatedVelocityBoundary<T,DESCRIPTOR, BulkDynamics>’ at the inlets and ‘setInterpolatedPressureBoundary<T,DESCRIPTOR, BulkDynamics>’ at the outlet.
I have been able to run the program using these boundary conditions, however when the initial conditions, at time 0, are visualised using ParaView these boundaries are not being shown as I had expected. Any suggestions regarding this issue would also be greatly appreciated.

Thank you in advance for your help,

Callum

[TimBingert]

Hi Callum,

are you sure you haven’t changed something about the case setup? When I download, unpack and compile OLB1.7 the waterAirflatInterface2d case works for me. This model uses an empirical Peng-Robinson equation of state with Huron-Vidal mixing rules, which will explain the parameters that you are wondering about.
About adding inlet and outlet boundary conditions: This model is designed to show how well this multi-component pseudo-potential can recreate thermodynamic equilibrium for the multi-component mixture. This model will need more specific implementation at least when it comes to the outflow/pressure boundary condition, as there won’t be a constant pressure at the outflow for such a multi-phase fluid because of surface tension effects.

I hope this can clarify your questions.

Tim

[CWhalley_1]

Hi Tim,

Thanks for the response, I will be sure to check out the Peng-Robinson equation of state with Huron-Vidal mixing rules to get a better understanding of the parameters. I have managed to get it working without any boundary conditions, I had made a few mistakes when altering the geometry.
Regarding the outflow is there a different boundary condition that I should try using that can be more easily implemented?

Kind Regards,

Callum

[TimBingert]

Hi Callum,

this outflow boundary condition topic is also a part of my current or future research, so I can’t give a final answer. But I read about a convective type boundary condition which might help in that case, but this is not more than a hint. Glad you managed to find your bug.

Kind regards
Tim

[CWhalley_1]

Hi Tim,

I did see the convection type boundary condition, I will have a look into implementing this into my model.
Thanks for your assistance and best wishes for your current and future research.

Thanks,
Callum

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