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Old   July 24, 2003, 04:07
Default Defining cell faces in BFC
Olof Liungman
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I have for many years pondered how the cell faces in a non-orthogonal BFC grid are defined. This is important when determining whether a particle is inside a certain cell, where the velocity components are situated and what the face area is.

Consider the following example: an otherwise cubic cell has three nodes on its LOW face at Z = 0.0, but the fourth at Z = -0.1, i.e. a little lower than the other three. These four nodes are then NOT on a plane. So how does PHOENICS define the LOW cell face?

One idea that a colleague came up with is as follows. Calculate the "mean" position of the four nodes in question (call it the center position, P). Then draw four triangles, each with its tip at P and bases along the four segments made up of the sides between the four nodes. We now have four well-defined planes (3D triangles), with well-defined areas and a (kind of...) center position P where the W velocity component may be placed.

Is this how PHOENICS does it?

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Old   July 24, 2003, 09:48
Default Re: Defining cell faces in BFC
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Hi Olof,

I also wondered about the same question - i.e., how nonplanar cell faces are dealt with - some years ago. Since I did not find an answer, I bypassed it altogether by FORCING planar cell faces during the (BFC) grid generation, e.g., by pure rotation of a planar grid. This was sufficient for my purposes, but it may be not general enough for your needs.

I hope this helps somewhat, Rami
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Old   July 28, 2003, 04:23
Default Re: Defining cell faces in BFC (Att. CHAM)
Olof Liungman
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Well, Rami, I suppose we are both eagerly waiting to hear CHAM's answer. Anyone from CHAM reading this? If so, please enlighten us.

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