Dear Muhammad Zahid,

You can calculate velocity in the x and y direction separately using LAMMPS. After getting your desired value, you can do a summation using an excel file.

For example:

compute cc1 flow chunk/atom bin/1d y 0.0 1.0

fix 1 flow ave/chunk 100 10 1000 cc1 vx vz norm sample file vel.profile

This might help you:

https://docs.lammps.org/compute_chunk_atom.html

https://docs.lammps.org/fix_ave_chunk.html