Energy Domain Imbalances for Multiphase flow

KMJ · September 8, 2010, 12:58

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

ghorrocks · September 8, 2010, 21:19

Interesting. No idea what is going on. I would talk to CFX support.

stumpy · September 9, 2010, 10:06

Could you post the energy imbalance summary from the end of your .out file?

KMJ · September 10, 2010, 08:33

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 %

ghorrocks · September 10, 2010, 09:06

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.

September 8, 2010, 12:58	Energy Domain Imbalances for Multiphase flow	#1
KMJ New Member Kasper Jonck Join Date: Mar 2009 Location: Copenhagen Posts: 2 Rep Power: 0	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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September 8, 2010, 21:19		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Interesting. No idea what is going on. I would talk to CFX support.

September 9, 2010, 10:06		#3
stumpy Senior Member Join Date: Apr 2009 Posts: 531 Rep Power: 21	Could you post the energy imbalance summary from the end of your .out file?

September 10, 2010, 08:33		#4
KMJ New Member Kasper Jonck Join Date: Mar 2009 Location: Copenhagen Posts: 2 Rep Power: 0	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 %

September 10, 2010, 09:06		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	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.