Reply To: Error Post-Processing Solution Data to Calculate Pressure and Viscous Forces

[wheeler.ky]

Hi Rob, thanks for the reply!

I performed some mesh refinement and ended up decreasing cell size on the walls by a factor of ten. Here's a picture comparing the old mesh on the wall (on the right), and the mesh after decreasing cell size 5x, so the final mesh I tested has a wall cell size that is half of the left side of the picture. And all walls were refined, the image is just for a comparison.

After running at the 10x refinement, Fluent gave me a net pressure force of 6.839022e-5 N and net viscous force of 4.0280261e-5 N. Exporting the solution data and performing the calculation described above gives me a net pressure force of 6.83902e-5 N and net viscous force of 3.95294e-5 N. This is about a 2% difference between the value I calculed and the value from Fluent, which is an improvement from the 5% from above. However, I still find it odd that I can only calculate the pressure forces (nearly) exactly and not the viscous forces. I also find it odd that the value seems to be converging towards the value I get when I export and calculate viscous forces, ie. the value from Fluent changed much more than the value I calculated when performing the mesh refinement. This seems to imply that exporting and calculating the forces is a better method since it might not require as fine of a mesh and it's starting to take a while to create the mesh with the refinements.

Again, thank you for the help and let me know if you have any more ideas about why I can't get the values to match closer.

Best,

Kyle