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May 26, 2009, 03:21 
VOF vs LSM

#1 
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Hi users
Would like to know if anyone did compared or studied on the VOF (volume of fluids) vs LSM (level set method) in free surface tracking? which method provided better accuracy and faster simulation time?
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July 7, 2009, 06:25 

#2 
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isabel
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I am studying nucleate boiling. Growing of a bubble in a liquid.
For my case, the level set method is more accurate than the VOF method 

July 8, 2009, 04:52 

#3 
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Hi Isabel
thanks for reply, so what CFD code that you are using and do you have any paper on this for sharing? thanks 

July 10, 2009, 12:13 

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isabel
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I am using OpenFOAM. If you are using it too, we can discuss doubts. My mail is lamasgaldo@yahoo.es


July 13, 2009, 21:31 

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Isabel
I know OpenFOAM is a open source CFD code but i didn't use it. do you have any paper/doc to compare the results between these two approaches? thanks in advance. 

July 15, 2009, 03:54 

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isabel
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July 16, 2009, 20:26 

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thanks and would like to know how OpenFOAM solve multiphase problem that involved free surface tracking? does it solve as one fluid problem employed by Flow3D or solve momentum equation for both air and fluid like others typical CFD code?


July 17, 2009, 03:09 

#8 
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isabel
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It is an open code, so you can program the equations you prefer.


July 17, 2009, 11:30 

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well that might be interest of academic research but may not for industrial application. anyway thanks for your info.


July 20, 2009, 13:52 

#10 
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matteo lombardi
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Hello Isabel,
I am trying to implement the levelset method for boatlike free surface problem but unfortunately quite unsuccesfully so far.. Could you please shedm me some light on the topic: what I ahve done is: I have started from rasInterfoam and mainly just substitued the gamma equation parts with the level set one and solve something like: solve ( fvm::ddt(gamma) + fvm::div(phi, gamma) ) I initialise gamma with funkysetFields and it is ok. So now gamma is the distance form the surface and i solve a simple transport equation for it (not the MULES...). I then reconstruct rho using: rho == (sign(gamma) scalar(1))/scalar(2.0)*rho1 + (scalar(1) +sign(gamma))/scalar(2.0)*rho2; and rhoPhi: surfaceScalarField phiGamma=fvc::interpolate(rho); rhoPhi = ((sign(phiGamma) scalar(1))/scalar(2.0)*rho1 + (scalar(1) +sign(phiGamma))/scalar(2.0)*rho2)*phi; Checking rho it seems ok. For some reason, although rho and gamma (the level set variable) seem ok , i have some pressure issues and almost form the start the simulation tends to diverge,mainly driven by pressure issues. I haven't implemented any reinitialization or similar since I don't think it is that necessary in this case, and anyway the problem doesn't come from that since the simulation divrges from the beginning. I know I have been very "brutal" in my formulation andh haven't implemented any stabilization or smoothing technique,but it is my first try and wanted to keep it simple. Do you have any suggestion to make it work? have you implemented something particularly different?any major error i have done? Thank you very much, ciao Matteo 

July 21, 2009, 04:07 

#11 
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isabel
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Hello Matteo.
I don't know what can be your problem. I am simulating nucleate boiling (growing of a bubble). What I have done is the following:  I started from solver interFoam, but instead of solving the gammaEqn, I solved the level set equation.  As you said, the initial condition of the level set function is the distance from the interface.  I have done reinitilialization and smoothing to improve convergence and accurate. 

July 21, 2009, 04:15 

#12 
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matteo lombardi
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Hey Isabel, thank you for the fast reply.
Have you done something particularly different than what i wrote? do you see any major error? Do you agree that in principle it shlould be working? How do you recontruct rho and rhoPhi exactly? I will add a bit smoothing and see if it there is any improvements.. Do you base your level set formulation on the paper by Shu? thanks, ciao matteo 

July 21, 2009, 04:32 

#13 
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matteo lombardi
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One more thing I have just noticed:
I haven't updated the value of the viscosity! Where is it done in interfoam? where do you do it in your level set formulation? Thanks, Matteo 

July 21, 2009, 05:04 

#14 
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isabel
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I have updated the viscosity at the same way as the density:
rho == H*rho1 + (scalar(1)  H)*rho2; mu == H*mu1 + (scalar(1)  H)*mu2; where H is the Heaviside function, which have been smoothed previously. 

July 21, 2009, 11:03 

#15 
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matteo lombardi
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Do you have any pressure/velocity peak issues with the level set formulation?
In my formulation, everytime a cell swap from air to water I have a big peak of pressure/velocity and that phenomena become unstable and slowly diverge.. I have smoothed the interface and thinks get better but still far worse than with the vof approach.. I imagine the problem is somewhere in the rhoPhi evaluation that is not smoot enough or something similar.. Is there any smoothing in the VOF approach of that term? or of Rho, or mu? thanks, Matteo 

July 22, 2009, 02:33 

#16 
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isabel
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I don't understand very well what is your problem. If you want send me your results to lamasgaldo@yahoo.es and I will try to help you if I can.


August 13, 2009, 22:59 

#17  
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michael barkhudarov
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Quote:
To be fair to the VOF method at large  has any one compared LSM in Openfoam with FLOW3D's VOF? Or have the comparisons been done with the VOF method in Openfoam only? 

August 14, 2009, 09:11 

#18  
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Quote:
Perhaps you should check your documentation  or the Flow3d help desk  for help on this one. 

December 7, 2009, 06:54 

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Hi all,
I have recently started OpenFOAM. I needed some papers, info about LSM in OpenFOAM. ak 

December 24, 2009, 14:18 

#20 
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private
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Your question is really pretty general, not specific to flow3d.
Have you tried posting it in the main forum? You'll probably get a lot more comment  and thus exposure to a wide variety of experience. 

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