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-   -   volume fraction in mixture model and VOF???? (http://www.cfd-online.com/Forums/fluent/48606-volume-fraction-mixture-model-vof.html)

 multiphase-flow June 25, 2008 21:27

volume fraction in mixture model and VOF????

3D model, using VOF and mixture model to simulate air-water flow in a vessel.

display contour of volume fraction of liquid phase on the vessel wall and cross section of vessel. What is the meaning of "volume" fraction of liquid on the wall? Is it surface coverage or the fraction of liquid in the cell next to the wall. The same question arises when I use XY plot for displaying volume fraction values on a line created by me. I don't understand how there is volume fraction (3D) on a line (1D)? Can someone explain the volume fraction for me. Thanks.

 Shehab Abdelrahman June 25, 2008 21:58

Re: volume fraction in mixture model and VOF????

hi there: the volume fraction of species is the ration between the substance's volume in the mixture and the total volume of the mixture. obviousely it is a 3D quantity. but in postprocessing, you can make any line and the fluent will interpolate the value of any variable at that line. this however, for some variables like volume fraction has no meaning. you must choose the suitable way to show your results. the suitable way for showing the volume fraction results I think is contour plotting.

 multiphase-flow June 25, 2008 22:26

Re: volume fraction in mixture model and VOF????

Thanks. one more question: contour plotting of volume fraction on the vessel wall or cross section of the domain (2D surface). Is it wrong to plot volume fraction on 2D surface? Do you mean the volume fraction can be only plotted for interior fluid in 3D model due to it is called "volume" fraction?

 Shehab Abdelrahman June 26, 2008 06:21

Re: volume fraction in mixture model and VOF????

no.. I didn't mean that. as you can get the volume fraction contours in a 2D or surface wall( surface wall is not by default a flat 2D plane..if the wall is cylinder then it is considered 3D)...what I told you that you can get any thing from the postpressoring, what ever in 1D, 2D or 3D the important thing is that it must be meaningful to the reader. let me give you an example. let you have a elbow-pipe that contain a flow of water and sand, and you want to see what is the volume fraction distribution over the the whle volume of the elbow-pipe. the postprocessor, will show you the volume fraction over the volume but it will only show you the outside contours. the internal contours will not appear. then you will have to get slices planes along the elbow-pipe to find the contours distribution inside the pipe and these will be usefull for showing the contours distribution inside the pipe. then, you want to know the volume fraction profile at axissymmetric line in the middle plane in the bending part of the pipe to see the variation in a axis symmetric position. thus, you will need to get a rack line to get the volume fraction profile along this line. so, the key word is what do you want to show from your results.

 Lao August 7, 2014 10:35

Volume fraction in 2D problem

Hi,

I cannot understand how does fluent calculate the volume fraction in a 2D problem, (2D axisymmetric problem). Should it be the same value than if I use 3D problem?

can anyone help help?

cheers,

Lao

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