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-   -   Simulation of cavitation flow:problem of heat transfer (https://www.cfd-online.com/Forums/cfx/107682-simulation-cavitation-flow-problem-heat-transfer.html)

 kiwishall October 4, 2012 01:46

Simulation of cavitation flow:problem of heat transfer

While I solve the cavitation flow of LNG with k-omiga turbulence model, the RMS of H-Energy in the result kept being 1.0e+01 after only five steps(the curve of heat transfer is obviously wrong),and the rate of convergence were both zero.The details were as follows:
OUTER LOOP ITERATION = 5 CPU SECONDS = 2.227E+03
----------------------------------------------------------------------
| Equation | Rate | RMS Res | Max Res | Linear Solution |
+----------------------+------+---------+---------+------------------+
| U-Mom-Bulk | 0.97 | 1.4E-04 | 1.3E-02 | 1.2E-01 ok|
| V-Mom-Bulk | 0.96 | 1.3E-04 | 1.9E-02 | 1.1E-01 ok|
| W-Mom-Bulk | 0.97 | 1.9E-04 | 2.7E-02 | 1.5E-01 ok|
| P-Vol | 0.87 | 1.2E-05 | 7.4E-04 | 5.2 9.1E-02 OK|
+----------------------+------+---------+---------+------------------+
| Mass-LNG | 0.93 | 2.5E-04 | 6.8E-02 | 6.1 2.2E-02 OK|
+----------------------+------+---------+---------+------------------+
| H-Energy-LNG |99.99 | NaN | 0.0E+00 | 0.0E+00 OK |
| H-Energy-lngs |99.99 | NaN | 0.0E+00 | 5.9 0.0E+00 OK |
+----------------------+------+---------+---------+------------------+
| K-TurbKE-Bulk | 0.96 | 2.8E-04 | 4.4E-02 | 6.0 3.1E-02 OK|
| O-TurbFreq-Bulk | 0.95 | 1.2E-04 | 4.1E-02 | 7.7 1.9E-02 OK|
+----------------------+------+---------+---------+------------------
OUTER LOOP ITERATION = 6 CPU SECONDS = 2.735E+03
----------------------------------------------------------------------
| Equation | Rate | RMS Res | Max Res | Linear Solution |
+----------------------+------+---------+---------+------------------+
| U-Mom-Bulk | 1.22 | 1.7E-04 | 1.4E-02 | 2.8E-01 ok|
| V-Mom-Bulk | 1.24 | 1.7E-04 | 2.1E-02 | 2.8E-01 ok|
| W-Mom-Bulk | 0.97 | 1.9E-04 | 2.4E-02 | 1.1E+00 ok|
| P-Vol | 8.43 | 1.0E-04 | 3.8E-03 | 5.2 9.6E-02 OK|
+----------------------+------+---------+---------+------------------+
+--------------------------------------------------------------------+
| ****** Notice ****** |
| A wall has been placed at portion(s) of an OUTLET |
| boundary condition (at 0.3% of the faces, 0.6% of the area) |
| to prevent fluid from flowing into the domain. |
| The boundary condition name is: Blade Outlet. |
| The fluid name is: LNG. |
| If this situation persists, consider switching |
| to an Opening type boundary condition instead. |
+--------------------------------------------------------------------+
| Mass-LNG | 8.05 | 2.0E-03 | 2.6E-01 | 6.1 5.1E-03 OK|
+----------------------+------+---------+---------+------------------+
| H-Energy-LNG | 0.00 | NaN | 0.0E+00 | 0.0E+00 OK |
| H-Energy-lngs | 0.00 | NaN | 0.0E+00 | 5.9 0.0E+00 OK |
+----------------------+------+---------+---------+------------------+
| K-TurbKE-Bulk | 1.15 | 3.3E-04 | 4.5E-02 | 6.0 4.6E-02 OK|
| O-TurbFreq-Bulk | 2.35 | 2.8E-04 | 7.3E-02 | 7.7 2.9E-02 OK|

 ghorrocks October 4, 2012 07:42

This looks like a complex model with cavitation, heat transfer and multiple phases. Have you started with a simple model and introduced the physics one bit at a time?

 kiwishall October 5, 2012 00:45

In fact,I have solved many cases about cavitation at different conditions. Sometimes the result I got looks very well.But for the case with different geometrics (nozzle angle),it won't work.Maybe if I change the reference state of the materials I used,it will work and I can get a result that looks reasonable .But this strategy doesn't fit any case .Do youknow the reason ? Will the reference point affect so much ? How could I avoid this wrong results with what proper settings?

 ghorrocks October 5, 2012 06:17

Do you think explaining what you are modelling might help? And while you are at it maybe what is different about this one compared to the ones which worked well? I think that might help :)

 kiwishall October 5, 2012 08:44

I have compared the result with those worked well .The unique difference is that I set the simulation with different reference point .If with a actual reference point , ref-enthalpy and ref-entropy ,only some cases could work well .If with automatic ref-point ,there will be more cases that will work will .If with none, the effect will get better . However there are still some cases that can't work will. That is the problem I want to know.In different cases ,everything is same except that the geometric has different nozzle angle. Thank you for your help!

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