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Unsure boundary settings. Solution always explode.

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Old   March 13, 2021, 09:32
Default Unsure boundary settings. Solution always explode.
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Gabriel Souza
Join Date: Mar 2020
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Hello everyone. Hope you all doing great.

I'm here asking for some help to setup my case. I'm trying to resolve it by myself for some weeks and I think I'm freaking out (I'm frustated ).

I'll try to explaing everything you need to know and I hope some of you can give me some light to solve my problem.

Basically, I'm trying to solve a fuel-burning domestic oven cavity, but it's way simpler than you can imagine. I'm not considering combustion or something like that. I'm modeling the flame as a inlet of hot air along my burner geometry.

What I'm doing it setting up the faces that represent the burner as inlets and setting the boundary conditions that, with help from tutorials and online search, felt correct. The thing is that when I start solving, the solution always diverge with temperatures going lower than they physically should until they explode negative and the solver stops.

With my experiences while learning to use OpenFOAM, this behavior is usually caused by bad boundary contitions. The way the boundaries are set fell correct but I'm so frustaded with this that there must be a ridiculous error that is causing all the problems that I can't see.

In the images you can see the feature edges (just to show the overwall geometry) and a detail of the burner. The bad cells that go crazy low temperatures are always in the burner surface.

More details:
1. I was able to run the case using a coarser mesh than the one in the files but when I go to finner meshs, it doesn't work.

2. I've tryed running without turbulence and it doesent work even in the coarser mesh.

3. The temperature lowers at the first time-steps, then it goes back to normal but at 1,5-2s of runTime it lowers and diverge.

4. I'm not sure if I'm running potentialFoam correctly but it showed no difference in the solution.

5. I believe that the problems are in the boundary conditions so I would love if you could check it for me

Explaining the boundaries:
Red (inlet_ar_frio): An open region, inletOutlet condition that can supply cold air if the flux create a negative pressure "sucking" air from the outside, or just overflow from the cavity.

Green (outlet_ar_quente): Is the hot air outlet of the oven. The excess of hot air in the cavity should go out throught that canal.

White (inlet*): Is the burner. The detailed image shows where it should supply hot air. I'm setting a velocity and a temperature for each face. The marked faces are highlighted in the image.

Other: The oblong geometries is part of the fake bottom of the oven, a solid region that separates the burner from the main cooking cavity. It is a sheet metal that exchanges heat with the air. The other collors are walls that are set as a externalWallHeatFluxTemperature, considering an arbitrary h and external 300K temperature just to model a energy loss in the system.

The project files are in the google drive link.

If you willing to help, don't hesitate to ask the questions needed.

I thank you so much if you can help me. I would love to pay for a professions help but I'm just a student and my country money is so weak that I just can't.

Thank you again.
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boundaries condition, chtmultiregionfoam, convection-diffusion, error, negative temperature

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