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Oscillation problems simulating a turbulent diffusion flame

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Old   August 28, 2014, 04:53
Default Oscillation problems simulating a turbulent diffusion flame
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Hello everyone,

I'm trying to model a turbulent diffusion flame using the OpenFOAM solver flameletFoam. It's a transient solver based on rhoReactingFoam and I'm using it to perform RANS-simulations with k-epsilon-model.

At the beginning I used a coarse grid and everything worked fine. After that I tried to refine the grid which has led to oscillations in my axial temperature profile. ParaFoam shows an oscillating pressure, too. Moreover, the residuals for pressure don't look really good. I added screenshots showing my mesh, the temperature profile and the residuals for p.

In this particular case, the grid has about 25000 cells. I think thats not much according to a combustion chamber with a length of 1000 mm and a diameter of 700 mm. The thin pipe on the left side represents the jet. I think this is the part where the problem is caused. I tried to remove it and used groovyBC to define a fully developed pipe flow and everything worked fine. Unfortunately, the results are not satisfying. Furthermore, I tried to change the boundary conditions, but this did not help.

I don't know how to solve my problem, perhaps you have some ideas. Thank you!

Attached Images
File Type: jpg Mesh.jpg (85.1 KB, 10 views)
File Type: jpg T_ax.jpg (27.7 KB, 12 views)
File Type: jpg residuals_p.jpg (66.7 KB, 18 views)
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Old   September 2, 2014, 02:25
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Sorry for posting again, but I need to fix this problem and I still don't have a clue how to do that... really no one here who can help?
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