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dpdt-term in energy equation of buoyantPimpleFoam |
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March 13, 2014, 03:53 |
dpdt-term in energy equation of buoyantPimpleFoam
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New Member
Jens Peterson
Join Date: Feb 2014
Posts: 4
Rep Power: 12 |
Hello all,
I am simulating a buoyancy-driven flowcase with large temperature gradients using the buoyantPimpleFoam solver in OF2.3. The fluid (water) is between 15C and 285C and its thermophysical properties are set using polynoms to have them vary with temperature: Code:
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: 2.2.0 | | \\ / A nd | Web: www.OpenFOAM.org | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; object thermophysicalProperties; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // thermoType { type heRhoThermo; mixture pureMixture; transport polynomial; thermo hPolynomial; equationOfState icoPolynomial; specie specie; energy sensibleEnthalpy; } dpdt off; // coefficients for water @ 70 bar mixture { specie { nMoles 1; molWeight 18; equationOfState { rhoCoeffs<8> (-652.130039068252 17.3072281049247 -0.0530706424954250 -4.46788703056841e-05 6.61015720039410e-07 -1.70342449898889e-09 1.94284389663358e-12 -8.64283583580195e-16); } thermodynamics { Hf 0; //heat of formation, input in J/kg Sf 0; //standard entropy J/kg/K //cp (J/kg) by definition not a function of pressure. CpCoeffs<8> (-123868.395198191 2386.30977759511 -18.8516975602727 0.0819407624259010 -0.000211924050467349 3.26503697953756e-07 -2.77731495587309e-10 1.00765751262485e-13); } transport { //dynamic viscosity kg/ms muCoeffs<8> (0.907124928631493 -0.0143820511516075 9.76703409945348e-05 -3.67596758496769e-07 8.27176723626825e-10 -1.11210240552212e-12 8.26794094903911e-16 -2.62140652993808e-19); //Thermal conductivity W/mK kappaCoeffs<8> (44.3118446931015 -0.773151693822239 0.00570642822582130 -2.29415112216040e-05 5.45444040085740e-08 -7.69316563660768e-11 5.97198703640727e-14 -1.97170654681780e-17); } } Since the equationOfState is set as icoPolynomial, this means we will have no compressibility in the fluid, which is fine since it is water we're dealing with here. However, simulating this WITHOUT the flag "dpdt off;" as seen above, leads to divergence almost for all cases I've tried. Simulating WITH the flag "dpdt off;" gives good results, and I'm happy with using that. My question is: where does this dpdt term come from? If we take a look at the source code for solving the energy equation in the buoyantPimpleFoam solver: Code:
{ 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) == radiation->Sh(thermo) + fvOptions(rho, he) ); EEqn.relax(); fvOptions.constrain(EEqn); EEqn.solve(); fvOptions.correct(he); thermo.correct(); radiation->correct(); } Any input on this matter, or the general apporoach of this problem, is appreciated. // Jens |
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