# solarLoad - results not coherent with analytical

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 March 3, 2022, 06:30 solarLoad - results not coherent with analytical #1 New Member   Matteo Quirino Join Date: Feb 2019 Posts: 6 Rep Power: 7 The case I use to test solarLoad is an aluminium cube with size 1 m within a cubic dummy fluid region with size 1.5 m (used to introduce solarLoad) representing deep space (i.e. T = 0K and vacuum). The solarLoad is set to be fixed in direction (x axis) and fixed with a value of 1400 W/m2 with no reflected rays and only one band in the spectrum (i.e. nBands 1) If the value of absorptivity and emissivity are equal the analytical solution is 253 K. The results given by the simulation are between 242 K and 245 K, quite far from the analytical solution. Furthermore, if the values of absorptivity and emissivity are changed but kept equal the solution changes. This should not be happening, if the ratio absorptivity/emissivity is one the solution should be still 253 K. The analytical solution is verified by using a workaround that does not use solarLoad: the dummy fluid region is split so that there is a region in front of the cube thus it is possible to simply set qro to 1400 in 0//qr file. In this case, changing the values of absorptivity and emissivity but keeping the ratio equal to 1 the solution does not change, that is coherent with analytical results. The values of the view factors for the geometry in exam are checked and coherent with analytical. The workaround of course cannot be applied to curved surfaces as the input flux has to be scaled according to the angle between the sun direction and the cell face normal. That is the reason why I want to use solarLoad Analytical solution: T = (q_sun/sigma * abosrptivity/emisivity * A_in_sun/A_tot) ^ (1/4) for a cube with equal values of absorptivity and emissivity the solution is T = (q_sun/sigma * 1/6) ^ (1/4) Can anyone explain this behaviour? I leave attached the files "boundaryRadiationProperties" and "radiationProperties" for the dummy fluid region called "space" "boundaryRadiationProperties" Code: ```/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: v2106 | | \\ / A nd | Website: www.openfoam.com | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; object boundaryRadiationProperties; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // ".*" { type transparent; wallAbsorptionEmissionModel { type multiBandAbsorption; emissivity (1); absorptivity (0); }; } space_to_cube { type opaqueDiffusive; wallAbsorptionEmissionModel { type multiBandAbsorption; emissivity (0.86); absorptivity (0.86); }; } // ************************************************************************* //``` "radiationProperties" Code: ```/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: v2106 | | \\ / A nd | Website: www.openfoam.com | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; object radiationProperties; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // radiation on; radiationModel viewFactor; solarLoadCoeffs { sunDirectionModel constant; sunDirection (1 0 0); sunLoadModel constant; directSolarRad 1400; diffuseSolarRad 0; // see solarCalculator.H for other model examples and details // Energy spectrum spectralDistribution (1); // Radiative flux coupling flags solidCoupled true; // Couple through Qr the solid regions (default true) wallCoupled true; // Couple through Qr wall patches (default false) // Reflecting rays useReflectedRays false; absorptionEmissionModel none; scatterModel none; sootModel none; } viewFactorCoeffs { smoothing true; //Smooth view factor matrix (use when in a close surface //to force Sum(Fij = 1) constantEmissivity true; //constant emissivity on surfaces. nBands 1; useSolarLoad true; } // Number of flow iterations per radiation iteration solverFreq 1; absorptionEmissionModel none; scatterModel none; sootModel none; // ************************************************************************* //``` Last edited by MatteoQ; March 4, 2022 at 05:45.

 August 16, 2022, 06:23 #2 Senior Member     Herpes Free Engineer Join Date: Sep 2019 Location: The Home Under The Ground with the Lost Boys Posts: 932 Rep Power: 12 Hello, Would you mind to share the entire case? Thanks. __________________ The OpenFOAM community is the biggest contributor to OpenFOAM: User guide/Wiki-1/Wiki-2/Code guide/Code Wiki/Journal Nilsson/Guerrero/Holzinger/Holzmann/Nagy/Santos/Nozaki/Jasak/Primer Governance Bugs/Features: OpenFOAM (ESI-OpenCFD-Trademark) Bugs/Features: FOAM-Extend (Wikki-FSB) Bugs: OpenFOAM.org How to create a MWE New: Forkable OpenFOAM mirror