Learning Forum

[Makara]

I have one question to discuss with you that I use fluent to run 2D channel flow and I get result of Volume flow rate at x=0m (Volumetric Flow Rate= -0.0001978993 m3/s) but My professor want me to calculate the Volume flow rate using Simpson 1/3 rule while using the Velocity at x=0 from solution data in fluent but after my calculation I got Volume flow rate at x=0m (Volumetric Flow Rate=0.000180 m3/s) and percentage difference is 9.04%. is it the same velocity which fluent use to calculate Volume Flow rate compare to the velocity that export from solution data of ASCII File that I used to calculate volume flow rate using Simpson 1/3 rule?

[Amine Ben Hadj Ali]

I do not trust 100% reporting on user defined planes or cross sections. Fluent is not solving for Volumetric Flow Rate.
Can you please add more details how you are using using the Simpson Law to get flow rate?

[Amine Ben Hadj Ali]

Flow rate will be Velocity times the area and the area along y will be the facet area for each U. Also try exporting using cell center values but again: user defined post-processing planes won't be accurate compared to boundary values (there is no facet area associated with them.)

[Makara]

Thank you for your advice. I use Simpson Law to get flow rate by export data on the node cross-section. and I apply Simpson 1/3 rule by using the velocity data from Ansys as I shown in attachment file.

[Amine Ben Hadj Ali]

Okay. Thank :)

[Makara]

Hello Sir
I have one more question about my 2D problem that I try to export X-velocity solution data using ASCII file type that I already create the node point. when I export using Cell center and node the result is much difference so how ANSYS calculate the Cell Center X-velocity in 2D? How can I convert Node to Cell Center?
Thanks
Best Regards
K. Makara

[Rob]

The values are usually fairly similar if the mesh is well refined. How different are the positions and x-velocity?

[Makara]

I used 3 node to export the data from fluent. The velocity when I export using Node it come up with Node 1= 0.00 m/s, Node 2=0.005m/s, Node 3=0.01 m/s. But we export using Cell center. it come up with Node 2=0.00916 m/s. so I still wonder where and how fluent calculate the Cell Center?
Thank you.
Best Regards
K. Makara

[Rob]

What value of x position does the cell centred value have?

[Makara]

I use X=0 with The cell centered value the same as Node Value. I just change the location of it only.

[Rob]

Plot both lines on the same graph in Excel and post the results.

[Makara]

Thank you for your reply.
boundary Condition I use No Slip Boundary condition. and Velocity inlet=0.01 m/s. For this Graph I plot the velocity at x=0m.

[Rob]

Showing a difference of 1%. Now replot with the x-position v y-position.

[Makara]

thanks for your fast reply.
The Velocity from At Y=3mm to 18mm is about 1% difference. But I if we compare between Y=1mm, 2mm and Y=19mm the difference is about 45%. and I use no slip boundary condition but there is still have x-velocity Y=0mm and Y=20mm too.

[Rob]

Which may be the interpolation onto the lines. How well refined is the mesh?

[Makara]

The Mesh that I use with 10 Vertical Mesh. So this mean that the Cell Center is interpolation from the Node? Or Somethings?
Thanks.
K. Makara

[Rob]

Pretty much. Double the resolution (use adaption) and try again.

[Amine Ben Hadj Ali]

Pretty much related as Rob mentioned to interpolation of the values to the line you created. I will be good to plot the lines in yellow colors on the last mesh picture you shared.

[Makara]

Thank you very much for you solution. Now I get the result between node and cell-center is about 1% different after use adaption. you are the best to me.

[Makara]

One more question. I have export all the node using ASCII file and I can see the node number in that file and I want to compare that node number with Fluent but I don't know the Node and Element number in Fluent. How could I see the Node number and Element number in fluent?

Thanks
best regards
K. Makara

[Makara]

[Rob]

I don't think you can. The node IDs change if you re-order the mesh so they're not used very much: we always focus on position.

[Makara]

Thank your for helping me.
Best Regards
K. Makara

[Amine Ben Hadj Ali]

I do not understand: do you want to see that node numbering in Fluent as contour? If yes: not possible out of the box. You can however show the cell ID in Fluent.

[Makara]

Thanks you for reply DrAmine.
I want to see the Node Number or Element number in fluent with x-velocity value. Because I want to compare the Node Number I have exported in ASCII file as I show you if it correct or not?

[Rob]

Why not compare the position?

[Amine Ben Hadj Ali]

You can post the node number: just compare as Rob mentioned with position. I sincerely think this step you are doing is not necessary: you are just losing your time trying to check if the values are correct.