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Helium jet instability using reactingFoam

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Old   January 18, 2017, 04:04
Default Helium jet instability using reactingFoam
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Anshul Lakhani
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Hello Foamers,

i am new to openfoam so kindly excuse my lack of knowledge.

i am trying to simulate a helium jet being fired into ambient using reactingfoam with chemistry and combustion switched off. Helium jets being significantly lighter than air are unstable and oscillate at a fixed frequency (like flow past a cylinder). A screenshot of the flow field showing the helium concentration is attached. (geometry is 2D- one cell in z direction).
To measure this frequency i am using a pressure probe at 3D location (D is diameter of inlet). what i expect from the pressure probe is that after the initial transients it would show a constant amplitude sinusoidal pressure signal, that is not the case ofcourse.

Even if i run the simulation for a long time, the jet doesnt seem to settle down (to uniform oscillations).
The reynolds number based on diameter is 1800 and it is run as a laminar case.
i have tried reducing the reynolds number, delta T, still the situation doesnt improve.
Although since it is PIMPLE algorithm, increasing the number of outer iterations improved the signal, but not to the desired level. the case files are also attached, kindly take a look and let me know what can be done.

Thank you,
Attached Images
File Type: jpg Screenshot from 2017-01-18 14-06-29.jpg (94.9 KB, 65 views)
File Type: jpg pressuresignal.jpg (61.5 KB, 34 views)
Attached Files
File Type: zip (179.1 KB, 21 views)
File Type: zip (77.0 KB, 20 views)
File Type: zip (10.5 KB, 45 views)
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Old   August 24, 2020, 23:40
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Abhijit Kushwah
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Hi Anshul, did you manage to improve the jet oscillation frequency? What were the boundary conditions? Can you please post your suggestion and modifications ?
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instability, laminarjet, openfoam, reactingfoam

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