# Study of the EEqn.H in rhoPimpleDyMFoam.

 Register Blogs Members List Search Today's Posts Mark Forums Read

 May 27, 2013, 08:03 Study of the EEqn.H in rhoPimpleDyMFoam. #1 New Member   Join Date: May 2013 Location: Santa Fé, Argentina Posts: 5 Rep Power: 5 Hi, I'm working with the solver "rhoPimpleDyMFoam" from the OpenFOAM 2-2-x version. In specific i was trying to replicate the polytropic process in an adiabatic compression. The case i studied is a pistone-cylinder sistem where air is compressed by the pistone patch which is a moving wall. The pistone velocity is adjusted to 0,1(m/s) to aproximate a reversible process. When i choose energy "he" as internal energy i could reproduce the polytropic process in an adiabatic compression. However when i choose energy "he" as entalphy I couldn't achieve the theoretical expression for air. Instead the system looks as it would be non adiabatic or like the conversion between work and internal energy was not made properly. Therefore i started to study the EEqn.H. I compare the theoretical balance of total energy in terms of entalphy with what is written in the EEqn.H. Balance of a tensorial property in an arbritary moving domain. Balance of mechanical energy. Balance of internal energy. The balance of internal energy can be expressed in terms of entalphy. Replacing in the balance of internal energy. Balance of total energy. The sum of the balances of mechanical and internal energy results in the balance of total energy. If the terms of work of viscous forces and the gravity are neglected, the balance is: rhoPimpleDyMFoam: EEqn.H The balance of total energy in the EEqn.H file with considered as entalphy is: Code: fvm::ddt(rho, he) + fvm::div(phi, he) + fvc::ddt(rho, K) + fvc::div(phi, K) - dpdt - fvm::laplacian(turbulence ->alphaEff(), he) == fvOptions(rho, he) Where, , is relative to the mesh. If fvOptions(rho, he) are considered as zero, the term from the final balance is no considered in EEqn.H. Then i try adding in the EEqn.H the therm . Code: fvm::ddt(rho, he) + fvm::div(phi, he) + fvc::ddt(rho, K) + fvc::div(phi, K) - dpdt + fvc::div(fvc::meshPhi(U),p) - fvm::laplacian(turbulence ->alphaEff(), he) == fvOptions(rho, he) The result was correct. As in the first case (he=internal energy) the adiabatic compression was reproduced with the relation . The question is, should the term be introduced in any way in fvOptions(rho, he) or it must be explicit in the EEqn.H? Thanks, Horacio mturcios777, fredo490, mgg and 1 others like this.

 June 12, 2013, 22:15 #2 Senior Member     Santiago Marquez Damian Join Date: Aug 2009 Location: Santa Fe, Santa Fe, Argentina Posts: 430 Rep Power: 16 Any clues?. It seems we have to upload the question to the bug tracker. Regards. __________________ Santiago MÁRQUEZ DAMIÁN, Ph.D. Research Scientist Research Center for Computational Methods (CIMEC) - CONICET/UNL Tel: 54-342-4511594 Int. 7032 Colectora Ruta Nac. 168 / Paraje El Pozo (3000) Santa Fe - Argentina. http://www.cimec.org.ar

 July 8, 2013, 18:43 #3 Senior Member     Santiago Marquez Damian Join Date: Aug 2009 Location: Santa Fe, Santa Fe, Argentina Posts: 430 Rep Power: 16 __________________ Santiago MÁRQUEZ DAMIÁN, Ph.D. Research Scientist Research Center for Computational Methods (CIMEC) - CONICET/UNL Tel: 54-342-4511594 Int. 7032 Colectora Ruta Nac. 168 / Paraje El Pozo (3000) Santa Fe - Argentina. http://www.cimec.org.ar

August 20, 2013, 08:33
#4
New Member

Join Date: Jun 2012
Posts: 11
Rep Power: 6
Hi,

I'm trying to simulate exactly the same case, but I get very unphysical solutions even using the internal energy formulation. I also tried your proposal concerning the EEqn.H file without any success.

You said you were able to reproduce the adiabatic compression, so I would appreciate it if you had a look at my settings or if you shared me your case.
Attached Files
 KammerExp.tar.gz (4.6 KB, 17 views)

September 4, 2013, 12:37
#5
New Member

Join Date: May 2013
Location: Santa Fé, Argentina
Posts: 5
Rep Power: 5
Quote:
 Originally Posted by ALU Hi, I'm trying to simulate exactly the same case, but I get very unphysical solutions even using the internal energy formulation. I also tried your proposal concerning the EEqn.H file without any success. You said you were able to reproduce the adiabatic compression, so I would appreciate it if you had a look at my settings or if you shared me your case.
Hi ALU,

I tried your case without modifying it and i get bad results too.

File: /0$U If you want to reproduce an expansion, you should set for the "top" velocity the same velocity of the "patch", in this case, 0.1 m/s for the third coordinate. Remember that the type "fixedValue" indicates absolute velocities. If you want to set relative to domain velocities you can use type "movingWallVelocity". File: /system$ fvSolution

I added in the subdictionary PIMPLE the flag "correctPhi" equal to "no".

The correctPhi equation makes the linear solver to diverge.

For compressible fluids, i think that this equation is no necessary as the non conservative effects due to the mesh change in the flux are absorbed by the density equation.

I run the case with a time step of 0.001s from time 0 to time 1s and the adiabatic expansion was obtained successfully.

Quote:
 Originally Posted by ALU I also tried your proposal concerning the EEqn.H file without any success
The modification of the EEqn.H is necessary when you set, in the dictionary "thermophysicalProperties" (in thermoType{}), the energy to sensibleEnthalpy, but we have here sensibleInternalEnergy.

Regards,

Horacio
Attached Files
 KammerExp-2.tar.gz (35.7 KB, 24 views)

 September 5, 2013, 02:20 #6 New Member   Join Date: Jun 2012 Posts: 11 Rep Power: 6 Hi Horacio Aguerre, thank you very much for the correction of my case and the detailed explanation, this really helps a lot! Regards

 September 11, 2013, 00:32 #7 Member   赵庆良 Join Date: Aug 2013 Posts: 56 Rep Power: 5 Hi ,Horacio Aguerre could you see my problem and tell some thing?I think you can answer my question.I moves fireFoam of 2.0.1 to 2.2.1,then rewrite hEqn according to the EEqn.H in fireFoam of 2.2.1 and other necessary codes.But ,when I wmake my rewrited fireFoam,it gives me errors:undefine div(phi,h) in fvscheme. The following is codes of EEqn.H: { volScalarField& he = thermo.he(); fvScalarMatrix EEqn ( fvm::ddt(rho, he) + fvm::div(phi, he) + fvc::ddt(rho, K) + fvc::div(phi, K) + ( he.name() == "e" ? fvc::div ( fvc::absolute(phi/fvc::interpolate(rho), U), p, "div(phiv,p)" ) : -DpDt ) - fvm::laplacian(turbulence->alphaEff(), he) == fvOptions(rho, he) ); EEqn.relax(); fvOptions.constrain(EEqn); EEqn.solve(); fvOptions.correct(he); thermo.correct(); Info<< "T min/max = " << min(T).value() << ", " << max(T).value() << endl; } There is div(phi,he) insteading of div(phi,h),So It should be no need to define (phi,h) in fvshceme,but define div(phi,he).However,I see the fvsheme in smallpoolfire2D of 2.2.1,there indeed is div(phi,h).In fact,there is the term of "div(phi,he)" in EEqn.H,why define div(phi,h) in fvsheme?I think I have some thing not understand.!

September 11, 2013, 09:11
Energy variables
#8
New Member

Join Date: May 2013
Location: Santa Fé, Argentina
Posts: 5
Rep Power: 5
Quote:
 Originally Posted by zqlhzx Hi ,Horacio Aguerre could you see my problem and tell some thing?I think you can answer my question.I moves fireFoam of 2.0.1 to 2.2.1,then rewrite hEqn according to the EEqn.H in fireFoam of 2.2.1 and other necessary codes.But ,when I wmake my rewrited fireFoam,it gives me errors:undefine div(phi,h) in fvscheme. The following is codes of EEqn.H: { volScalarField& he = thermo.he(); fvScalarMatrix EEqn ( fvm::ddt(rho, he) + fvm::div(phi, he) + fvc::ddt(rho, K) + fvc::div(phi, K) + ( he.name() == "e" ? fvc::div ( fvc::absolute(phi/fvc::interpolate(rho), U), p, "div(phiv,p)" ) : -DpDt ) - fvm::laplacian(turbulence->alphaEff(), he) == fvOptions(rho, he) ); EEqn.relax(); fvOptions.constrain(EEqn); EEqn.solve(); fvOptions.correct(he); thermo.correct(); Info<< "T min/max = " << min(T).value() << ", " << max(T).value() << endl; } There is div(phi,he) insteading of div(phi,h),So It should be no need to define (phi,h) in fvshceme,but define div(phi,he).However,I see the fvsheme in smallpoolfire2D of 2.2.1,there indeed is div(phi,h).In fact,there is the term of "div(phi,he)" in EEqn.H,why define div(phi,h) in fvsheme?I think I have some thing not understand.!
Hi zqlhzx,

The EEqn is able to solve the energy balance in terms of enthalpy ("h") or internal energy ("e"). Both balances have common expresions. For this expresions it is used the generic energy variable "he". However the expresions differ. Then appears the conditional statement that selects the appropiate source term for the respective form of energy.

Code:
 he.name() == "e"
Then "he" is like as a generic energy that is used in the definition of the EEqn, but in fact it is "h" or "e".

In fvSchemes and in fvSolution you must set for the energy parameters the name "he.name()"

If you choose enthalpy "he.name()=h" you must define "div(phi,h)" in fvSchemes.
If you choose internal energy "he.name()=e" you must define "div(phi,e)" in fvSchemes.

In the OpenFOAM official web site there is an explanation on how to set up the thermophysical properties.
HTML Code:
http://www.openfoam.org/docs/user/thermophysical.php
Regards,

Horacio

 September 12, 2013, 04:05 #9 Member   赵庆良 Join Date: Aug 2013 Posts: 56 Rep Power: 5 Thanks ,Horacio Aguerre!It is kind of you!

 September 13, 2013, 09:34 #10 Member   赵庆良 Join Date: Aug 2013 Posts: 56 Rep Power: 5 Dear Horacio Aguerre: Thank you for your last reply!I have another problem I would like to consult you.In my thermophysicalPropertise,I want to define thermo type like this: thermoType { type hePsiThermo; mixture reactingMixture; transport sutherland; thermo janaf; energy absoluteEnthalpy; equationOfState perfectGas; specie specie; }I want use "absoluteEnthalpy;",but when I run my case,it tells me have no this thermo combination.I found just "psiuReactionThermo" Class can use absoluteEnthalpy. "psiReactionThermo"and "rhoReactionThermo"can not use absoluteEnthalpy.They only have sensibleEnthalpy.My case have chemical reaction and I must use absoluteEnthalpy,can you give me advise how to change my thermo type?Thanks again!

 October 11, 2013, 13:43 #11 Senior Member     Santiago Marquez Damian Join Date: Aug 2009 Location: Santa Fe, Santa Fe, Argentina Posts: 430 Rep Power: 16 Henry changed the code using the snippet suggested by Horacio, but in pEqn.H https://github.com/OpenFOAM/OpenFOAM...d6c6406b07d7bb Regards. __________________ Santiago MÁRQUEZ DAMIÁN, Ph.D. Research Scientist Research Center for Computational Methods (CIMEC) - CONICET/UNL Tel: 54-342-4511594 Int. 7032 Colectora Ruta Nac. 168 / Paraje El Pozo (3000) Santa Fe - Argentina. http://www.cimec.org.ar

 Tags rhopimpledymfoam

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post hamid1 FLUENT 1 August 4, 2013 00:14 [ANSYS Meshing] grid study, important questions hamid1 ANSYS Meshing & Geometry 2 February 10, 2012 14:28 pggow FLUENT 0 December 21, 2011 15:31 bhanwar Main CFD Forum 0 September 29, 2011 08:21 Mario Main CFD Forum 0 August 24, 2009 09:59

All times are GMT -4. The time now is 15:34.