August 10, 2023 at 9:13 amDominik BuksaSubscriber
Hello. I have a question about the Peclet number. My geometry is very irregular and I would like to know if there is advection anywhere in the flow. How can I calculate the Peclet number? Or can ansys count it? Should the characteristic dimension of this number be the size of the cell?
August 10, 2023 at 10:30 amRobAnsys Employee
Have a look at the full Peclet Number definition re characteristic dimension. Fluent has functions to calculate pretty much anything of interest, but you'd need to add the length scale into that yourself as these are determined at the cell level, and the cells don't have any information other than for that cell. Ie there is no domain diameter/length etc value in the cell.
August 10, 2023 at 11:34 amDominik BuksaSubscriber
I understand, but each cell has a different characteristic dimension and a different local velocity value. Can I read, for example, the average or something in the fluent so that I can get the result?
I understand the approach to each cell but with a million elements it is a big problem.
August 10, 2023 at 11:40 amDominik BuksaSubscriber
Can ansys tell me e.g. the smallest cells and their dimensions? So I could manually count the Perclet number at critical places.
August 10, 2023 at 11:42 amRobAnsys Employee
How would you calculate the value in an experiment? That's usually the better way to approach nondimensional numbers with a length scale in simulation: cell size is very variable in most models.
August 10, 2023 at 11:48 amDominik BuksaSubscriber
August 10, 2023 at 12:33 pmRobAnsys Employee
What do you need the number for? Ie experimental comparison. Dimensionless numbers tend to be used to compare designs so you "just" need to pick a length scale that makes sense for your needs.
August 10, 2023 at 1:24 pmDominik BuksaSubscriber
I wanted to calculate the Pereclet number because I read on CFD forums that it must be less than 2 for the solution to be stable.
Additionally, I wanted to know what part is advection and what part is diffusion.
August 10, 2023 at 2:30 pmRobAnsys Employee
I'd not seen that one. I tend to go with, are the monitor points changing, how are the residuals and do the fluxes balance.
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