[Kirill-MIPT]

Hello!

I'm trying to load my real gas model to Fluent, but I cannot even make the ideal gas equation of state work, even though I had taken the UDF for it from the User Guide (7.16.5 in the User Guide). For my problem I have P=15000 Pa, T=120 K at the inlet. The proper value of density for this model must be rho~0.436 kg/m3, but Fluent intializes it with value of rho=2.35E-5 kg/m3 in almost all cells and with value of rho~5E+7 kg/m3 in one cell. The process of calculation lasts for 0 iterations with Courant number CN=0.001, then I have:

Divergence detected - temporarily reducing Courant number to 1e-08
and trying again...

Error: Internal error at line 1596 in file '..\..\src\rp_mstage.c'.
Divergence detected in AMG solver

Error: Internal error at line 1596 in file '..\..\src\rp_mstage.c'.
Divergence detected in AMG solver
Error Object: #f


I loaded and compiled the library as it was written in the Guide. Could you please help me with this problem?

Regards, Kirill

[KaLium]

Did you study the limitations of that code?

Are you using mass-flow inlet?

[Kirill-MIPT]

Originally Posted by KaLium

Did you study the limitations of that code?

Are you using mass-flow inlet?

Yes, I studied all the limitations. The only boundary conditions for my problem are pressure-inlet, pressure-outlet and wall. I also used pressure-based solver.

For my problem the total pressure value is 6E7 Pa and total temperature is 1200 K. This corresponds to hypersonic flow with Mach number M~7. Could this problem type somehow influence the solution process with Pressure-based solver?

Regards

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[Светлана]

Perhaps you could try the real gas model on a simplified simulation first? For example, create a straight rectangular pipe and try the real gas model in that.

[Kirill-MIPT]

Originally Posted by Светлана

Perhaps you could try the real gas model on a simplified simulation first? For example, create a straight rectangular pipe and try the real gas model in that.

Thank you for your response! I tried a number of simple geometries (a pipe too). Using each of them gave me no results - every time the density field was initialized with inappropriate value in all cells but one (40 vs 0.43 kg/m3) and a VERY inappropriate (maybe it's a junk cell in cell/face array) value of 3e8 kg/m3. The calculation crashed on the first iteration. It seems strange, because I used the same code for ideal gas EOS as it was given in the Guide.

I also tried to run the calculation for a small number of iterations (for example 10) with the built-in ideal gas EOS and after that I turned on the real gas model (that was supposed to model the same gas with the same EOS). I monitored the evolution of static pressure, density, temperature and velocity fields. The temperature field started crashing after the very first iteration. I guess there's something wrong with energy equation? The other fields started crashing some more iterations later (I guess the crashing temperature field influenced them).

Looking forward to your response! Regards

Update: I tried this EOS on three different computers with three different versions of Fluent. There were the same problems

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[Kirill-MIPT]

Thanks to all - I used a code for real gas model for a too early version of Fluent. The code for 15th version differs from it a bit. Now the example model works

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[Светлана]

Congratulations, that was easy

[liuso]

hallo, i have the same Problem , can u tell me , where can i find the new code for 15th Version ?
thanks

Originally Posted by Kirill-MIPT

Thanks to all - I used a code for real gas model for a too early version of Fluent. The code for 15th version differs from it a bit. Now the example model works

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[Kirill-MIPT]

Hello! You may find the code in the User Guide in chapter 7.6.15. The chapter name is User Defined Real Gas Model.