SimScale CAE Forum

Difference in values from simulation and analytical solution

Hello I’m a student and currently still relatively new to engineering physics and CFD! I was trying to simulate a simple laminar flow of air in a straight cylindrical pipe, but for some reason I could not obtain the same results of velocity that I obtained in the analytical solutions through my own calculations of the fluid velocity at the centre. Would appreciate any help.

Hey there, and welcome!

Could you please share with us the link to your project. A description of your analytical results and how they compare would also be helpful.

We have a validation case that should help:

Hi sorry here’s the link for the project i was working on: https://www.simscale.com/workbench/?pid=1937217207349067454

WIth regards to the analytical solution, I was calculations for reynolds number as well as a simplified version of Poiseuille flow (highly unsure if this is the right term as I’m still learning, apologies if im quoting it wrongly) but the final equation I used to calculate my max velocity is in the image attached below.

image

Did you already generate a plot of velocity vs. radius?

Can you please share your numerical values? How large is the deviation?

I can notice from the mesh that you are not getting a cell at the center of the pipe. This causes the peak value to not be captured by the model, thus the maximum reported corresponds to the adjacent locations (notice the constant value across the cells at the center):

The curve plot might help to see the overall results and spot if the center cell is the only missing part. You can create such curve by sampling a few points on the radial direction. Create a cutting plane somehow in the middle of the pipe for this!