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-   -   two different gas! Fluid pair model! (https://www.cfd-online.com/Forums/cfx/240604-two-different-gas-fluid-pair-model.html)

saha2122 January 14, 2022 14:49
two different gas! Fluid pair model!
 
Hi every body:)
I want to model a domain with two gas.
the first inlet has ideal air but the second inlet has ideal Air (99%) and CO2 (1%).
in the basic setting of domain, in fluid and particle definition, I defined two gas.
this is the first time that I model this.
in the 'fluid pair model', how I should fill the parameters like as 'interface Len. Scale' and the other parameters???:confused:

is there any body help me?

Opaque January 14, 2022 15:21
What are you trying to model? Multiphase flow, or multicomponent flow?

I think you mean the latter, but not clear about your goals

saha2122 January 15, 2022 13:01
Hi dear Opaque
yes I want to model multi component using CFX.
Co2 is the trace gas.

Opaque January 16, 2022 18:33
Then, you need to first create a Variable Composition Mixture

Inset Material, Option/Variable COmposition Mixture, select materials for the mixture

Insert Domain, Insert Fluid, Select Mixture Material you created,

Continue setting up the models.

There is no concept of Fluid Pair for a mixture.

saha2122 February 9, 2022 02:15
Dear Opaque

as you suggested I used variable component mixture that contains CO2, N2, O2, Ar and Ne.
I got some warnning in the CFX solver.




+--------------------------------------------------------------------+
| Table bounds warnings at: END OF TIME STEP |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| |
| Independent variables went out of bounds while computing the |
| variables listed below using table interpolation. In each case |
| the bounds error was handled by clipping or extrapolation. |
| If this situation persists, consider increasing the table range. |
| |
+--------------------------------------------------------------------+
| |
| Location Name : WS1 |
| Mesh location : VERTICES |
| Routine : UPD_LOCALE_PROP1 |
| Partition : 2 |
| Variable Name : N2.Static Enthalpy |
| Ind. Variable : Absolute Pressure |
| Bound : Lower |
| Min Value : -3.5883E+06 |
| Handled By : Clipping |
| |
+--------------------------------------------------------------------+
| |
| Location Name : WS1 |
| Mesh location : VERTICES |
| Routine : UPD_LOCALE_PROP1 |
| Partition : 2 |
| Variable Name : N2.Static Enthalpy |
| Ind. Variable : Temperature |
| Bound : Lower |
| Min Value : 1.1836E+00 |
| Handled By : Extrapolation |
| |
+--------------------------------------------------------------------+
| |
| Location Name : WS1 |
| Mesh location : VERTICES |
| Routine : UPD_LOCALE_PROP1 |
| Partition : 2 |
| Variable Name : CO2.Static Entropy |
| Ind. Variable : Temperature |
| Bound : Lower |
| Min Value : 1.1836E+00 |
| Handled By : Clipping |
| |
+--------------------------------------------------------------------+
| |
| Location Name : WS1 |
| Mesh location : VERTICES |
| Routine : UPD_LOCALE_PROP1 |
| Partition : 2 |
| Variable Name : CO2.Static Entropy |
| Ind. Variable : Absolute Pressure |
| Bound : Lower |
| Min Value : -3.5883E+06 |
| Handled By : Clipping |
| |
+--------------------------------------------------------------------+
| |
| Location Name : WS1 |
| Mesh location : VERTICES |
| Routine : UPD_LOCALE_PROP1 |
| Partition : 2 |
| Variable Name : Ne.Static Entropy |
| Ind. Variable : Absolute Pressure |
| Bound : Lower |
| Min Value : -3.5883E+06 |
| Handled By : Clipping |
| |
+--------------------------------------------------------------------+
| |
| Location Name : WS1 |
| Mesh location : VERTICES |
| Routine : UPD_LOCALE_PROP1 |
| Partition : 2 |
| Variable Name : Ne.Static Entropy |
| Ind. Variable : Temperature |
| Bound : Lower |
| Min Value : 1.1836E+00 |
| Handled By : Clipping |
| |
| |
| Location Name : WS1 |
| Mesh location : VERTICES |
| Routine : UPD_LOCALE_PROP1 |
| Partition : 2 |
| Variable Name : Ar.Static Enthalpy |
| Ind. Variable : Temperature |
| Bound : Lower |
| Min Value : 1.1836E+00 |
| Handled By : Extrapolation |
| |


|
| Location Name : WS1 Rotating Wall |
| Mesh location : BELG16/IP |
| Routine : MINMAX |
| Partition : 2 |
| Variable Name : O2.Static Enthalpy |
| Ind. Variable : Absolute Pressure |
| Bound : Lower |
| Min Value : -1.0354E+06 |
| Handled By : Clipping |
| |
+--------------------------------------------------------------------+
| |
| Location Name : WS1 Rotating Wall |
| Mesh location : BELG14/IP |
| Routine : MINMAX |
| Partition : 2 |
| Variable Name : Ar.Static Enthalpy |
| Ind. Variable : Temperature |
| Bound : Lower |
| Min Value : 5.3673E+00 |
| Handled By : Extrapolation |
| |
+--------------------------------------------------------------------+
| |
| Location Name : WS1 Rotating Wall |
| Mesh location : BELG16/IP |
| Routine : MINMAX |
| Partition : 2 |
| Variable Name : Ar.Static Enthalpy |
| Ind. Variable : Absolute Pressure |
| Bound : Lower |
| Min Value : -1.0354E+06 |
| Handled By : Clipping |
| |

| Location Name : V1 Shroud |
| Mesh location : BELG20/IP |
| Routine : MINMAX |
| Partition : 1 |
| Variable Name : CO2.Static Enthalpy |
| Ind. Variable : Absolute Pressure |
| Bound : Lower |
| Min Value : -9.1043E+04 |
| Handled By : Clipping |
| |
+--------------------------------------------------------------------+
| |
| Location Name : V1 Shroud |
| Mesh location : BELG20/IP |
| Routine : MINMAX |
| Partition : 1 |
| Variable Name : O2.Static Enthalpy |
| Ind. Variable : Absolute Pressure |
| Bound : Lower |
| Min Value : -9.1043E+04 |
| Handled By : Clipping |
| |
+--------------------------------------------------------------------+
| |
| Location Name : V1 Shroud |
| Mesh location : BELG20/IP |
| Routine : MINMAX |
| Partition : 1 |
| Variable Name : N2.Static Enthalpy |
| Ind. Variable : Absolute Pressure |
| Bound : Lower |
| Min Value : -9.1043E+04 |
| Handled By : Clipping |
| |
+--------------------------------------------------------------------+
| |
| Location Name : V1 Shroud |
| Mesh location : BELG20/IP |
| Routine : MINMAX |
| Partition : 1 |
| Variable Name : Ar.Static Enthalpy |
| Ind. Variable : Absolute Pressure |
| Bound : Lower |
| Min Value : -9.1043E+04 |
| Handled By : Clipping |
| |
+--------------------------------------------------------------------+
| |
| Location Name : V1 Shroud |
| Mesh location : BELG20/IP |
| Routine : MINMAX |
| Partition : 1 |
| Variable Name : Ne.Static Enthalpy |
| Ind. Variable : Absolute Pressure |
| Bound : Lower |
| Min Value : -9.1043E+04 |
| Handled By : Clipping |
| |
+--------------------------------------------------------------------+
| |
| Location Name : inlet WS1 |
| Mesh location : BELG105/IP |
| Routine : MINMAX |
| Partition : 2 |
| Variable Name : CO2.Static Enthalpy |
| Ind. Variable : Absolute Pressure |
| Bound : Lower |
| Min Value : -1.2847E+06 |
| Handled By : Clipping |
| |

+--------------------------------------------------------------------+
| |
| Location Name : WS1 |
| Mesh location : VERTICES |
| Routine : CAL_GVar |
| Partition : 1 |
| Variable Name : Ne.Static Entropy |
| Ind. Variable : Absolute Pressure |
| Bound : Lower |
| Min Value : -4.7072E+05 |
| Handled By : Clipping |
| |
+--------------------------------------------------------------------+
| |
| Location Name : WS1 |
| Mesh location : VERTICES |
| Routine : CAL_GVar |
| Partition : 1 |
| Variable Name : O2.Static Entropy |
| Ind. Variable : Absolute Pressure |
| Bound : Lower |
| Min Value : -4.7072E+05 |
| Handled By : Clipping |
| |
+--------------------------------------------------------------------+
| |
| Location Name : WS1 |
| Mesh location : VERTICES |
| Routine : CAL_GVar |
| Partition : 1 |
| Variable Name : CO2.Static Entropy |
| Ind. Variable : Absolute Pressure |
| Bound : Lower |
| Min Value : -4.7072E+05 |
| Handled By : Clipping |
| |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
| Newton's method warnings at: END OF TIME STEP |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| |
| Newton's method failed to converge while computing the variables |
| listed below. In each case, the solver continued with the variable |
| field as it was on the final iteration. |
| |
| If this situation persists, you might try decreasing the Newton |
| iteration underrelaxation factor. This can be changed by setting |
| one of the following parameters for your mixture: |
| |
| Temperature : "Constitutive Relation Under Relaxation" |
| Pressure : "Newton Pressure Under Relaxation" |
| |
+--------------------------------------------------------------------+
| |
| Location Name : WS1 |
| Mesh location : VERTICES |
| Routine : UPD_LOCALE_PROP1 |
| Partition : 2 |
| Variable Name : Temperature |
| Last 3 Changes : 3.18867E+00 1.93066E+00 1.16286E+00 |
| Tolerance : 1.0000E-02 |
| Status : STALLED |
| Max Iterations : 100 |
| |
+--------------------------------------------------------------------+

saha2122 February 9, 2022 02:16
dear Opaque
may you please help me?

ghorrocks February 9, 2022 05:37
CFX calculates material properties using a look up table which spans a temperature and pressure range you define. Your error messages are saying the the simulation temperature and/or pressure went out of the range in your material property tables, meaning that it cannot accurately predict material properties. This means your simulation results are likely to be wrong or diverge. In your case it looks like it diverged.

To fix:
* Improve convergence by smaller time steps, double precision numerics, tighter convergence criteria.
* Make the table range wider. But only do this if the table does not cover the range you expect the fluid to cover.
* Use a simpler material model. Use fixed properties, incompressible fluids if possible. If you need compressible fluids then start with ideal gas and once that is working change over to your actual gas model.

Opaque February 9, 2022 07:15
Not sure exactly which material definition you picked to create your mixture. But, I (like Glenn usually advices) start simple, and increase complexity so you can pinpoint when a problem/issues is introduced into your model.

Here would be my approach,
1 - Simple material, N2 is best run until converges
2 - If (1) was successful, create a mixture with N2, and O2. Set inlet to pure N2, no O2. Running again, solution convergence should be nearly identical and final results should be IDENTICAL, not close.
3 - Set some O2 at the inlet, rerun, any issues? No, continue adding materials to your mixture as needed, only one at a time.


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