Question

What is the “sweeping velocity” of a turbulent flow?

Answer 1

Since they mention that the sweeping velocity pertains to the energy containing range it must be the r.m.s. velocity of turbulent flow and not its mean velocity. Mean velocity, more precisely its gradient, is merely an energy source that sustains turbulence.

Answer 2

The turbulent flow of particles is a normal thing to be taken as a experiment in the forces as the particles flow from higher to lower concentration