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Energy Domain Imbalances for Multiphase flow

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Old   September 8, 2010, 11:58
Default Energy Domain Imbalances for Multiphase flow
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KMJ
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Kasper Jonck
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Hi,

I am performing a multiphase simulation with 2 phases, an oil and a gas.
It is set up with the Homogenous Eulerian-Eulerian model. There is no interphase mass transfer.
I am solving for Total Energy as the viscous work needs to be included. The homogenous heat transfer model is used.

My simulation runs with no problem and the residuals converge below 1e-6.
The Domain Imbalances are below 1% for all variables except the Energy-equation for the two phases. Both show considerable imbalances in the range 20 to 100 %.

I have noticed that the actual value of the imbalances are very close and I suspect the imbalances are simply the transfer of energy from one phase to another.
The CFX manual states that for the Homongenous Heat transfer model the solver "solves a separate enthalpy equation for each fluid with a large interphase heat transfer term which forces the temperature fields to be the same". This fits with my assumption regarding the imbalance.

However I have been unable to find anything in the manual (or elsewhere) to confirm my assumption, i.e. that this Imbalance can be ignored if and conservation is upheld as long as the actual values of the energy imbalances are the same.

Any help is appreciated.

/KMJ
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Old   September 8, 2010, 20:19
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Glenn Horrocks
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Interesting. No idea what is going on. I would talk to CFX support.
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Old   September 9, 2010, 09:06
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Could you post the energy imbalance summary from the end of your .out file?
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Old   September 10, 2010, 07:33
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Here are the Energy imbalance summaries.


+--------------------------------------------------------------------+
| H-Energy-Hydraulic Oil |
+--------------------------------------------------------------------+
Boundary : Inlet 6.9201E+04
Bnd Src/Visc Work: Inlet 8.8562E+00
Bnd Src/Visc Work: Outer rotor 1.1336E+04
Boundary : Outlet -1.4390E+05
Bnd Src/Visc Work: Outlet -2.1738E-01
Bnd Src/Visc Work: Rotor 4.4608E+04
Domain Src (Neg) : Highboost -5.8653E+05
Domain Src (Pos) : Highboost 4.0112E+05
-----------
Domain Imbalance : -2.0415E+05

Domain Imbalance, in %: -34.8073 %

+--------------------------------------------------------------------+
| H-Energy-Air |
+--------------------------------------------------------------------+
Boundary : Inlet 5.6279E+02
Bnd Src/Visc Work: Inlet 2.1116E-03
Bnd Src/Visc Work: Outer rotor 5.1827E+03
Boundary : Outlet -1.4346E+03
Bnd Src/Visc Work: Outlet -3.3962E-04
Bnd Src/Visc Work: Rotor 1.7349E+04
Domain Src (Neg) : Highboost -1.4890E+04
Domain Src (Pos) : Highboost 2.0030E+05
-----------
Domain Imbalance : 2.0707E+05

Domain Imbalance, in %: 103.3800 %


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Old   September 10, 2010, 08:06
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It does suggest you are right, the interphase component is not included. But this is probably a good thing for a homogenous energy equation model - for this assumption to be valid there should not be large interphase heat transfer.

I suspect this is telling us the homogeneous assumption for the energy equation is not valid and you need to move to a non-homogeneous model.
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