curvature at the interface (interFOAM)
Hi all,
my question ist about the curvature calculation in interFoam. The magic happens in interfaceProperties.C and was also discussed often in the Forum. Anyhow, I still have an open question. The curvature is calculated by K_ = -fvc::div(nHatf_); in the simple expression which is ok for me. Before that, the gradient of alpha is determined on the cell faces by interpolation from the cell-gradient of alpha. Afterwards, the face-unit interface normal flux is calculated (nHatf_ = nHatfv & Sf;) and used for the calculation of the curvature as written above. But... I couldn't find out, how this divergence is realized. The Doxygen linked me to an explanation which is not helpful for me. I also set up a dummy hex 3x3 case an tried to understand the calculated value for the curvature in the central-cell, but did not succeed. I'll be glad for any advices. Greetings Lindstroem |
Hi Lindstroem, respect to the code of fvc::div, in gaussConvectionScheme.C we have:
Code:
00110 template<class Type> Code:
00042 template<class Type> Regards. |
Hi Santiago,
thanks for your help. But doesn't the GaussConvectionScheme need two parameters (faceFlux and vf)? in the interfaceProperties it is only called with one argument (nHatfv_). The reason why I am digging through that, is that I wanted to calculate the sum of the curvature over a circle which should analytically be 1/r. If I sum up the K_ in the interfaceProperties it results in sth. about 10e-6 where the analytical solution would be 6.6. Do you know the reason for that? Greetings |
Right. You are calling fvc::div. You can see it also calls fvc::surfaceIntegrate.
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Hi Anton,
thanks, I think I got it :) Greetings |
Hi again,
I would like to specify the question posted above. I have a 2D case with a bubble. If I sum up the curvature in interfaceProperties.C Code:
K_ = -fvc::div(nHatf_); Has anyone did the same and can tell me what I did wrong? Thanks! Lindstroem |
How did you initialize the shape?
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setFields with cylinderToCell
Code:
cylinderToCell |
From what I know it's better to start with a non-equilibrium shape (e.g. a box), relax the shape and then evaluate the resulting curvature.
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Thanks for your comment. Just tried that:
The sum of the curvature starts with -6.802736e-11 and ends with -9.166001e-12. Should be something about 4. //edit: seems to be known: http://www.openfoam.org/mantisbt/pri...php?bug_id=158 |
I don't understand why you want to check the accuracy of computed curvature in that way. Actually, at the interface of the droplet, at every point the curvature should be 1/r. I do not think summation of the interface curvature will equal 1/r. It should be n/r where n is the number of points in the summation.
Regarding to the curvature, you should note that the curvature vary quite a lot in interfoam. If you take the average of the curvature at the iso-surface of alpha1 = 0.5, you will get a value close to the value 1/r. Since the interface is smeared over 3-4 cells approximately, at cells with alpha1 = 0.9 or 0.1, you still have curvature different than 0. Therefore summing the curvature of cells belonging to the interface also can not give a proper result. Hope it is clear for you. |
Hello Duong,
i got your point - absolutely right that summing up would result in sth like n/r. Thanks for your comment! Lindstroem |
Hi again,
I'd like to ask one more detail to my initial question concerning fvc::div(): Is it true, that we calculate the second derivative (the divergence) only at the centroid point of the cells using the first derivative (the gradients) from the faces? |
To me divergence and second derivative refer to two different things...
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ok, sorry, the divergence of the gradient...
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