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How to simulate the water boiling by Level-Set method
Posted 2012年7月19日 GMT-4 19:53 Fluid & Heat, Computational Fluid Dynamics (CFD) Version 3.5a, Version 4.2, Version 4.3a 6 Replies
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I am trying to use the Level-Set method. However, I was frustrated by many times of failure.
My problem is how to deal with the interface using weak form contribution.
Level set and Phase field can deal with the multi-phase flow well.
But, if the phase change at the interface happens, weak form equations have to be used to.
In the Phase field example,
the weak form contribution is test(psi)*phi_source+test(p)*usource.
1) I want to know why used test(psi) and test(p) as the test function?
I used test(phips) and test(u) respectively, the results change a lot. But I don't know why. I might know how to get the weak form from strong form, but I don't know how and why to choose the exact test function.
2) I derived the level set form, and tried to add correct weak form to simulate the boiling phase change.
But the results were totally wrong, So, can somebody help me find the way to understand the level set weak form or give me some examples.
Thank you!
Hello Junxiang Shi
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did you manage to solve the problem? I am stuck with the same issue. I really cannot figure out the concept of weak form, and I don't know how should I change the source term if I want to solve the boiling water problem with level set instead of phase field.
If you have resolved the situation, I appreciate if you could share your solution to this problem.
regards,
Shawn
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I tried to get the source term according my understanding of Weak Form. But I failed.
Weak form is powerful, but not easy to use. :(
I have another problem on the phase change simulation in COMSOL.
Whatever Phase Change Field and Level Set Method, an interface is necessary to start the simulation, which means an initial bubble or droplet has to be patched.
If I am not interested in the heterogeneous boiling, but the homogeneous boiling process, COMSOL cannot help me, so I go back to FLUENT again.
What a pity!
If anyone has experience on this topic and share here, I will appreciate.
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I am in the same situation Junxiang was in originally. I am reading up on both phase field and level set theory to try and reformulate the boiling water problem and run it using the Level Set method. The major confusion for me is the usage of the weak expression (mostly the usage of the test functions).
I greatly appreciate it if you could let me know what exactly needed to be altered to run it effectively using Level Set.
Thanks,
Alex
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Hello,
I am in the same situation Junxiang was in originally. I am reading up on both phase field and level set theory to try and reformulate the boiling water problem and run it using the Level Set method. The major confusion for me is the usage of the weak expression (mostly the usage of the test functions).
I greatly appreciate it if you could let me know what exactly needed to be altered to run it effectively using Level Set.
Thanks,
Alex
Hello,
I am trying to simulate boiling water in a sealed pipe in 0.1 atm pressure. Not yet successful with Comsol. Anybody knows how to do it?
--
mep
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I had exactly the same problem than you, I mean, I couldn´t understand why they used these test functions in particular. I contacted with the support service and they helped me with this.
If you take a look to the weak expressions (Fluid properties->equation view), at the bottom, you can see how the equations are implemented in the weak form. For instance, the continuity equation,
, is implemented as -tpf.divu*test(p), where tpf.divu=ux+vy. Notice, that the test function is the pressure, so if you want to add a weak contribution to this expression, you shoud have to multiply by the same test functions. For this reason, when you try with another test funtion, you get so different results. Best regards
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This might be stupid question but could anyone help me to evaluate Delta interface function for level set with expression just as how it was described for phase field in boiling water example
Delta = 6*tpf.Vf2*(1-tpf.Vf2)*0.5*sqrt(phipfx^2+phipfy^2+eps) .
I am little confused .
Delta =6*sqrt(phils-phlils^2+eps)*sqrt(philsx^2+philsy^2+eps).
can anyone tell me if the above expression is right or wrong .