1. Theoretical background and experimental results

1.1 Motion of solid particles in a fluid

Various flow regimes of the fluid around the solid govern the movement of the particles, opposing them with a resistance that varies with the relative velocity of the solid in relation to the fluid. These are defined (figure 1 ) [1] :

• a laminar or Stokes regime (figure 1 a ) when relative motion is slow; the liquid threads, motionless in contact with the particle, are driven by a velocity that increases with distance from the particle,...