CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   CFX (http://www.cfd-online.com/Forums/cfx/)
-   -   Real Gas table generation (http://www.cfd-online.com/Forums/cfx/134380-real-gas-table-generation.html)

omidiut April 29, 2014 01:50

Real Gas table generation
 
Hi all
i have usual problem when i simulate real gas flow, peng-robinson or RK model.
this problem is " temperature and absolute pressure table range".
for some absolute and pressure range solver diverged and return errors like:

Newtons method failed to converge in 100 iterations. This |
| occurred while computing the following variable: |
| |
| Variable Name : Total Temperature |
| Location Name : NOZZLE |
| Mesh location : VERTICES |
| Mesh entity : |
| Last 3 Changes : 1.73755E+01 1.71344E+01 1.70618E+01 |
| Tolerance : 1.0000E-02 |
| |
| The Newton iteration was either slowly converging or has stalled. |
| The solver will continue with the variable set as it was on the |
| final iteration. If this situation continues you might try |
| increasing the number of iterations allowed for Newtons method. |
| This can be changed by setting one of the parameters: |
| |
| Temperature : "Constitutive Relation Iteration Limit" |
| Pressure : "Newton Pressure Iteration Limit" |
| |
| for your mixture using the definition file editor. |
+--------------------------------------------------------------------+



i generate this range by try and error! is there any relation for set this ranges?

Best regards

ghorrocks April 29, 2014 03:38

These sort of errors are common with complex equations of state. You need to improve your simulation's numerical stability. You can do this by:
* Better mesh quality
* Better initial conditions
* double precision numerics
* smaller time steps
* lower order differencing in space and/or time (this one will reduce the accuracy of your simulation)


All times are GMT -4. The time now is 03:32.