Transient super-sonic jet into (near) vacuum
Hello foamers,
currently I'm trying to simulate a super-sonic jet in (near) vacuum. The application is a gas target in an heavy ion accelerator. I'm interested in what density distribution the ion beam sees. I do not aim for perfect reproduction of reality, but to get a general gist of it, as the density in the accelerator is not easily measured. Later on the simulation should get more sophisticated of course (geometry and so on). I want to focus now to get the simulation stable with realistic parameters and go for more accurate schemes, models, and so on later. If anyone has already general advice on how to simulate such a setup I would appreciate it very much. Below I will describe more detailed my current problem/situation. So my domain looks like this: http://s10.postimg.org/8bd68ogfp/image.png Bottom is a symmetry plane, right and top are outlets, left bottom is the inlet, otherwise left is a wall. It's 2D (front and back are empty). For now I have chosen the sonicFoam solver with laminar turbulence model. My boundary conditions are mainly p: fixedGradient inlet, wavetransmissive outlet u: pressureinletVelocity inlet, zeroGradient outlet T: fixedGradient inlet, zeroGradient outlet FvSchemes are mainly linear or first order schemes. I think the main problem in my simulation are the high pressure gradients (up to ~10MPa at the inlet, vacuum something like ~1Pa), so I was trying to increase the inlet pressure slowly from run to run and see what resolutions (dt,dx) I need to increase or which problems pop up. What I observe in my latest run is that the simulation runs fine (no errors), but the calculated pressure just "freezes" at some point. It looks like this http://s10.postimg.org/g5dru2o8l/image.png and for some reason doesn't advance further. So why is that? What do I have to focus on to get my simulations stable? Finally some of my questions are:
Thank you very much in advance for any advice. EDIT: Btw while there are some posts I found on similar topics, they didn't help me too much. I tried using the knowledge given there and basically got to the results above. |
Hi, i'm interested in testing my compressible solver. If you will share your case data with me, i can try to run it
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thank you for the answer. Sure I can share my case data with you. However, it is not a realistic case as I'm currently still trying to figure out OpenFOAM, stability, typical errors etc. What kind of solver are you working on? Below I summarized some points I learned in the past week. These focus mainly on simulation of high pressure gas injection into near vacuum. Hopefully this helps people running into the same problems. Forgive me (and correct me) if I'm wrong. I'm nowhere near my goal in terms of knowledge and results.
Cheers Oli |
Hi mkraposhin,
Thank you for your attemp to look into the testing of the solver. I have uploaded my case file and I am simulating it in pisoCentralFoam developed by you. The solver produces unrealistic results near the shock wave region. Can you please look into it. I have generated the geometry exactly similar to the experiments and validated it using fluent. "Stationary supersonic plasma expansion: continuum fluid mechanics versus direct simulationMonte Carlo method" by S E Selezneva et.al. 2002 J. Phys. D: Appl. Phys. 35 1362 I have uploaded the case file here describing the error observed. I have also attached the small modification done for rho and P for avoiding negative pressure value and hence divergence of simulation. http://www.cfd-online.com/Forums/ope...ntralfoam.html I have uploaded the final data file to after simulation was completed in the below link in google drive: https://drive.google.com/file/d/0B5_...ew?usp=sharing Thank you, Chirag |
I will also share the fluent files if required which will help in the complete validation with commercial and openfoam.
I have validated the case with both steady and unsteady simulation using both pressure and density based solver. |
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