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Energy equation in rhoCentralFoam (revisited) |
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May 31, 2016, 08:54 |
Energy equation in rhoCentralFoam (revisited)
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#1 |
Senior Member
Join Date: Sep 2015
Location: Singapore
Posts: 102
Rep Power: 11 |
Hello everyone,
I am a bit confused about the energy equation implementation in rhoCentralFoam. Particularly, why does the viscous term 'sigmaDotU' appear in the (supposedly) Euler equation? Code:
surfaceScalarField sigmaDotU ( "sigmaDotU", ( fvc::interpolate(muEff)*mesh.magSf()*fvc::snGrad(U) + (mesh.Sf() & fvc::interpolate(tauMC)) ) & (a_pos*U_pos + a_neg*U_neg) ); solve ( fvm::ddt(rhoE) + fvc::div(phiEp) - fvc::div(sigmaDotU) ); - Kuragnov flux scheme is derived for strictly hyperbolic equations which are the Euler equations in this case - 'a_pos' and 'a_neg' are calculated using the eigenvalues of Euler equations and hence, the flux scheme should not be applied to the viscous term 'sigmaDotU' However, when I modified the solver by removing the viscous term from this equation and introducing it in the internal energy/enthalpy equation later, the results were not as good as the current solver (more diffusion, shocks were not sharp, unexpected flow separation). So, I am guessing that whatever the current solver is doing is correct but I can't seem to understand why. There are two other threads that I managed to find asking the exact question but both remain open: 1. Viscous terms in rhoCentralFoam 2. energy equation in rhoCentralFoam I am hoping that someone would point in the right direction. Thanks to all! |
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April 30, 2018, 11:46 |
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#2 |
Member
K
Join Date: Jul 2017
Posts: 97
Rep Power: 9 |
Did you find any answer for your questions ? I have the same exact questions.
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May 2, 2018, 01:10 |
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#3 |
Senior Member
Join Date: Sep 2015
Location: Singapore
Posts: 102
Rep Power: 11 |
Hi Mary,
I am afraid that I do not have a complete answer but let me give my opinion and, hopefully, someone will confirm/correct it. The first thing to note is that if the case is inviscid, then muEff=0. So, the term 'sigmaDotU' does not have any effect on the results for inviscid flows. The second thing to note is that the energy equation is solved using a predictor step for rhoE: Code:
fvm::ddt(rhoE) + fvc::div(phiEp) - fvc::div(sigmaDotU) Code:
fvm::ddt(rho, e) - fvc::ddt(rho, e) - fvm::laplacian(turbulence->alphaEff(), e) a_pos and a_neg are essentially interpolation factors to compute an intermediate state at each face based on the pos and neg values obtained by TVD reconstruction. So, (a_pos*U_pos + a_neg*U_neg) can be seen as some intermediate velocity Ustar. This intermediate velocity is used in the calculation of 'sigmaDotU'. Code:
surfaceScalarField sigmaDotU ( "sigmaDotU", ( fvc::interpolate(muEff)*mesh.magSf()*fvc::snGrad(U) + (mesh.Sf() & fvc::interpolate(tauMC)) ) & (a_pos*U_pos + a_neg*U_neg) ); Cheers, USV |
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July 5, 2018, 06:52 |
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#4 |
Member
K
Join Date: Jul 2017
Posts: 97
Rep Power: 9 |
Thanks a lot USV. Your explanation clarifies my question very well.
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September 6, 2024, 08:51 |
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#5 |
Member
Carmelo Baronetto
Join Date: Dec 2023
Posts: 30
Rep Power: 2 |
Hi to everyone,
sorry to resume this old post, but I noticed a detail in the energy equation I can't figure it out. I don't understand why in the term: Code:
surfaceScalarField sigmaDotU ( "sigmaDotU", ( fvc::interpolate(muEff)*mesh.magSf()*fvc::snGrad(U) + (mesh.Sf() & fvc::interpolate(tauMC)) ) & (a_pos*U_pos + a_neg*U_neg) ); Code:
fvc::interpolate(muEff)*mesh.magSf()*fvc::snGrad(U) Thank you so much |
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energy equation, openfoam, rhocentrafoam |
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