[Prudviraj]

Dear sir iam working on water flowing over the cylinder using 2D VOF multiphase flow transient model......I want to calculate water falling film thickness over the cylinder at various angles. please, someone, suggest a way to find water film thickness at various angles using CFD Post pro/plot/any other way.

Attached few images for better understanding.

Your support will be highly appreciated.
Volume fraction of water path lines full geometry.jpg

Contours of Volume fraction of water full geometry.jpg

[vinerm]

There could be multiple ways to do that in both, Fluent and CFDPost. One way of doing this in Fluent is, of course, via UDF but only if you are well conversant with it. Another way is to define the center of each cylinder as the origin of the cell zone and then report product of volume fraction of liquid and radial coordinate as well as angular coordinate. You have to do it twice, once with origin at upper cylinder's center and then with the origin at lower cylinder's center. Similar approach can be used in CFDPost by defining new coordinate systems at centers of the cylinders.

[Prudviraj]

Dear sir thanks for the positive response. I found one method in the research article. Iam attaching images of how they adopted a method to calculate film thickness over the cylinder. Iam a beginner to the CFD. Can you please read the attached images and elaborate.

Please elaborate...

CFD POST measurement lines.JPG

CFD POST measurement lines data.JPG

film thickness paper reference.JPG

[vinerm]

Their method is similar to what I have explained but much more involved and requires creation of lines at various angles. To create lines at such angles, you will anyway have to create local coordinate systems. And then you have to plot volume fraction on these lines along with length of these lines, which you have to keep fixed.

The method I explained does not require any such thing and will give you result directly.

[Prudviraj]

Thanks for the speedy response.....I am a beginner to the CFD....can you please elaborate more.....can you please elaborate for upper cylinder...I will proceed accordingly...........

Your support will be highly recommended.........

[vinerm]

Within Fluent, there is Cell Zone Condition panel. If you open, there is a place to provide origin location. Set the values of x and y to the center of either upper or lower cylinder. Then, go to Contours and plot radial coordinate. You will find this under Mesh. If origin is set properly, you will find concentric circles centered around the coordinates you specified as origin. If that is correct, then you need to define a custom field function. This is available under User Defined. Custom field function should be product of liquid volume fraction and radial coordinate. Then you can plot contour of this custom field function. You will observe value going only up to a certain thickness because beyond that liquid volume fraction is 0.

[Prudviraj]

Dear sir, thanks for your guiding........I have tried using cell zone condition panel and custom field function which is a product of water volume fraction and radial coordinate....I have attached (results) reference image....can you please elaborate next steps to find water film thickness at various angles over the cylinder....

FFF.1-12-06361.jpg custom field function.jpg

[Prudviraj]

Dear sir, thanks for your guiding........I have tried using cell zone condition panel and custom field function which is a product of water volume fraction and radial coordinate....Also please tell how to find angular coordinate(option iam not finding)....I have attached (results) reference image....can you please elaborate the next steps to find water film thickness at various angles over the cylinder....

Attachment 76607[/QUOTE]

[vinerm]

Actually, the custom field function is not required. Create an iso-surface with volume fraction 0.5. This will give you a line showing the edge of film. However, this will run throughout the domain, from top to bottom. You need to then use iso-clip to clip this iso-surface using the vertical coordinate. First clip should cover the bottom cylinder and second clip should cover the top cylinder. Now, you can plot an xy plot using these clips wherein you can choose angular coordinate for abscissa and radial coordinate for the ordinate or vice-versa. You can also export this plot if you want to plot it externally. You have to plot it separately for second cylinder since you have to change the origin location to the center of the second cylinder.

[Prudviraj]

Sir can you please check my second post and images attached...... I found in one of the research articles.....Can you please elaborate if it is easy for beginners....

[vinerm]

As per that article, you need to create two coordinate systems in CFDPost, one each at the centers of the cylinders. Then you need to create multiple lines at different angular coordinates for both the cylinders.

Then you can export product of volume fraction and radial coordinate to define thickness and angular coordinate for angle. The resolution will depend upon the number of lines you create. More lines, maximum up to the number of cells in the circumferential direction, imply better resolution for the graph.

[Prudviraj]

sir can you please elaborate.... i have created an isosurface with volume fraction of water 0.5..... iam following your instructions in CFD post....but no where iam not getting option angular coordinate and radial coordinate....please elaborate sir..... i have attached an image for your reference.....I want to find water film thickness at various angles....

FFF.jpg

[vinerm]

CFDPost does not have these coordinates directly available. Those need to be defined as expressions. That's why Fluent was preferable because it has both coordinates pre-defined. In CFDPost, you need to define radial coordinate as



and angular coordinate as



and then create two variables to which you can assign these expressions.

[Prudviraj]

Originally Posted by vinerm

Actually, the custom field function is not required. Create an iso-surface with volume fraction 0.5. This will give you a line showing the edge of film. However, this will run throughout the domain, from top to bottom. You need to then use iso-clip to clip this iso-surface using the vertical coordinate. First clip should cover the bottom cylinder and second clip should cover the top cylinder. Now, you can plot an xy plot using these clips wherein you can choose angular coordinate for abscissa and radial coordinate for the ordinate or vice-versa. You can also export this plot if you want to plot it externally. You have to plot it separately for second cylinder since you have to change the origin location to the center of the second cylinder.

Dear sir please elaborate above suggested method.... i have created iso surface in solution tab....please explain how to find angular coordinate in solution tab.......i got observed as per your suggestions instead of CFDpost , solution tab is better I mean more predefined functions available....please elaborate and suggest where angular coordinate option is available?

[vinerm]

These are available under Mesh. For contours of volume fraction, you selected Phases. In place of Phases, if you select Mesh, you will have both, radial as well as angular coordinates, available. You can use the same under Plots > XY Plot. Select the newly created isosurface and plot angular or radial coordinate. You can even plot both, one on x-axis and the other on y-axis. Do note that for an iso-surface, coordinates will be good only for that particular cylinder whose center point is given as the origin in cell zone conditions. That's why I asked you to clip the iso-surface into two parts; one for upper and another for lower cylinder. Then, instead of using iso-surface for the plot, you can use iso-clips for plotting the XY plot. Iso-surface needs to be generated before you can use Iso-Clip to clip the generated iso-surface. Iso-Clip generates a new surface and does not interfere with the existing iso-surface.

[Prudviraj]

Dear sir, Thanks for your support....can please clarify how to set angles.. i mean if I want to calculate water film thickness for every 10 degree or 20 degree or 30 degree.....

[vinerm]

You do not need to set angles. You can directly plot the angular coordinate along the iso-surface, preferably iso-clip. Read about these here

https://www.afs.enea.it/project/nept...ug/node874.htm

[Prudviraj]

Originally Posted by vinerm

These are available under Mesh. For contours of volume fraction, you selected Phases. In place of Phases, if you select Mesh, you will have both, radial as well as angular coordinates, available. You can use the same under Plots > XY Plot. Select the newly created isosurface and plot angular or radial coordinate. You can even plot both, one on x-axis and the other on y-axis. Do note that for an iso-surface, coordinates will be good only for that particular cylinder whose center point is given as the origin in cell zone conditions. That's why I asked you to clip the iso-surface into two parts; one for upper and another for lower cylinder. Then, instead of using iso-surface for the plot, you can use iso-clips for plotting the XY plot. Iso-surface needs to be generated before you can use Iso-Clip to clip the generated iso-surface. Iso-Clip generates a new surface and does not interfere with the existing iso-surface.

Dear sir, I have tried using isosurface and isoclip..i have created isosurface volume fraction of water 0.5 and I have used isoclip to clip isosurface.....later I have plot radial coordinate on X axis and isoclip on Y axis....results not getting iam attaching here.....

I have tried in CFD Post by creating lines........but I don't have command over the CFDPost.....

Please suggest a method or alternative......I need to find water film thickness over the cylinder for every 10 degrees...Currently iam working for one cylinder that to iam using symmetry option...

Your suggestions will be highly appreciable....


FFF-1-01000.jpg

FFF-1-01000.jpgcylinder.jpg

FFF-1-01000.jpgcylinder.jpginterior surface body.jpg

FFF-1-01000.jpgcylinder.jpginterior surface body.jpgvoulme fraction.jpg

FFF-1-01000.jpgcylinder.jpginterior surface body.jpgvoulme fraction.jpgvof.jpg

[vinerm]

As you observed, if you choose cylinder wall, a vertical line is plotted. That is expected since whole of the cylinder wall is at one radius; given by the radial coordinate where the line is plotted.

Similarly, when you plot for iso-clip, it should, for most of its part, be a vertical line since thickness would be more or less constant throughout the circumference. But to observe it, you should use radial coordinate on y-axis and and angular coordinate on x-axis. In any case, before you plot an XY Plot, display the iso-clips using Mesh Display or Contour Display to ensure that the iso-clip is certainly passing through the center of the gas-liquid interface. If it is not, then the iso-clip is not correct. Do note that you have to select the iso-surface of volume fraction 0.5 to create iso-clip.

[Prudviraj]

Originally Posted by vinerm

As you observed, if you choose cylinder wall, a vertical line is plotted. That is expected since whole of the cylinder wall is at one radius; given by the radial coordinate where the line is plotted.

Similarly, when you plot for iso-clip, it should, for most of its part, be a vertical line since thickness would be more or less constant throughout the circumference. But to observe it, you should use radial coordinate on y-axis and and angular coordinate on x-axis. In any case, before you plot an XY Plot, display the iso-clips using Mesh Display or Contour Display to ensure that the iso-clip is certainly passing through the center of the gas-liquid interface. If it is not, then the iso-clip is not correct. Do note that you have to select the iso-surface of volume fraction 0.5 to create iso-clip.

Dear sir, I have tried as per your suggestions...but results are not satisfying....can you please suggest more or alternative method to find film thickness over the cylinder.....I have attached one graph related to one of the research papers for your reference....

falling film thickness measurement graph.JPG