how to get distance between particle and center of channel
 

Hello everyone,
I'm interested in calculating the distance between particles and the center of channel by UDF, because I want to know the location of particle in the cross section of channel to calculate the lift coefficient. I know we can use POS_P(p) to get the position of tracked particles, however, since my model is a planar spiral channel with fixed width and height, for a certain particle, the coordinate of the corresponding vertcial centre plane of the channel keep changing. I just wonder if there is any approach to solve the problem. Thank you very much for your kind help in advance.

Hanks