UDF coming cells
 

Dear Fluent experts, good afternoon!

Please, tell me which way to dig, or maybe someone has encountered this and can tell.

The story is this. I supplement the solver by calculating some of the quantities I need, one of the terms of which is this thing:

ux*dSigma/dx=ux*((sigma(c-1)-sigma(c+1))/2deltax)

s-1 - cell "lower" on the axis, s + 1 - cell "higher" on the axis. - by itself conditionally.

I plan to replace the derivative of the quantity with its finite-difference analogue. However, here's the misfortune, how to find the nearest cells? As for the delta x, I understood roughly - if I know the number of the adjacent cell, I can find the coordinates of the centers of the cells and find the distance between them through C_CENTROID (x, c, t), it will suit me.

I tried to export the centers of the cells with their numbers, and realized that the cell with the number +1 could be in any direction. So you need to understand how to find the numbers of all adjacent cells.

Hope to help! Thanks in advance

Clarity
 

The description you provided is not very clear, such as, the statement,

however, if you are struggling with ID of the cell, then you can fetch IDs using C_ID, just like you fetch centroid using C_CENTROID. ID returned by C_ID is global.