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compressible and incompressible twophaseeulerfoam's UEqn is the same?

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Old   December 29, 2014, 07:05
Default compressible and incompressible twophaseeulerfoam's UEqn is the same?
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Dongyue Li
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Hi guys,

right now I was comparing the codes of openfoam 22x and 23x. cuz it provides different result. see more details here:

http://www.cfd-online.com/Forums/ope...ty-result.html

For now lets discuss the codes for openfoam 22x.

I found that the UEqn in twophaseeulerfoam and compressibleTwoPhaseEulerFoam is the same...

this formula is for compressibletwophaseeulerfoam:


this is for incompressible:


So the difference is that incompressible's UEqn are multiplied with alpha_1 and the density is reduced.

what confuse me is that both solvers use this incompreesible velocity equation.


if we neglect the R.H.S of the equation. this is twophaseEulerFoam:
Code:
U1Eqn =
        (
            
                fvm::ddt(U1)
              + fvm::div(phi1, U1, "div(phi1,U1)")
              - fvm::Sp(fvc::div(phi1), U1)

          - fvm::laplacian(nuEff1, U1)
          + fvc::div(Rc1)

          + fvm::div(phiR1, U1, "div(phi1,U1)")
          - fvm::Sp(fvc::div(phiR1), U1)
          + (fvc::grad(alpha1)/(fvc::average(alpha1) + scalar(0.001)) & Rc1)
         ==
compressibleTwoPhaseEulerFoam:
Code:
U1Eqn =
        (
            fvm::ddt(alpha1, U1)
          + fvm::div(alphaPhi1, U1)
          - fvm::Sp(fvc::ddt(alpha1) + fvc::div(alphaPhi1), U1)

          - fvm::laplacian(alpha1*nuEff1, U1)
          + fvc::div(alpha1*Rc1)
         ==

        );
if we do some rearrangements(multiply alpha1 in the incompressible UEqn), we can see this is the same

so does that mean in compressible two fluid model this density can also be reduced? or?

Thanks!
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