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SonicFOAM: field fluctuations at high pressure in 2D

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Old   May 13, 2015, 09:44
Default SonicFOAM: field fluctuations at high pressure in 2D
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Dear all, i am running the SonicFOAM to simulate a density profile with a gradient inside the gas target. When i was running 3D simulation, the results in the end was not looking physically correct, even the target volume wasn't filled completely, just like simulation slows down and stopped far in advance before reaching the steady state. When i was applying low pressure (2 and 4 mbar) results seems to be more close to the steady state, than results with 200 and 400 mbar respectively.

The target design itself is quite complicated and it has a small aperture with diameter of 300 microns and width of 100 microns, which defines the smallest cell in the simulation. But since a whole target is quite big (20*20 mm transversal size and 70 mm length), the difference in the cell size is big to save the computational time.

To get the proper results i built 2D model of the central slice of this target. Now within the same mesh results for the low pressure looks nice and stable, but at hight pressure i got a huge fluctuations in the field. On this forum i found that the reason for this could be the combination of high pressure with a small timestep. Suggestion was to increase the timestep, but i cannot do this due to the Courant number limitation at the smallest cells. I would be very grateful, if someone will tell me what are the limitations for the simulations with high pressure at small structures and how can i solve this problem to get the steady state? I am not an experienced user of OpenFOAM, but this results are in the crucial importance of the target development for the plasma accelerators and for my research in particular.

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density gradient, fluctuations, mesh anisotropy, small timestep, sonicfoam

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