This paper presents experimental measurements of the approach and rebound of a
particle colliding with a wall in a viscous fluid. The particle's trajectory was controlled
by setting the initial inclination angle of a pendulum immersed in a fluid. The
resulting collisions were monitored using a high-speed video camera. The diameters
of the particles ranged from 3 to 12 mm, and the ratio of the particle density to fluid
density varied from 1.2 to 7.8. The experiments were performed using a thick glass
or Lucite wall with different mixtures of glycerol and water. With these parameters,
the Reynolds number defined using the velocity just prior to impact ranged from 10
to approximately 3000. A coefficient of restitution was defined from the ratio of the
velocity just prior to and after impact.
The experiments clearly demonstrate that the rebound velocity depends on the
impact Stokes number (defined from the Reynolds number and the density ratio)
and weakly on the elastic properties of the material. Below a Stokes number of
approximately 10, no rebound of the particle occurred. For impact Stokes number
above 500 the coefficient of restitution appears to asymptote to the values for dry
collisions. The coefficients of restitution were also compared with previous experimental
studies. In addition, the approach of the particle to the wall indicated that the
particle slowed prior to impacting the surface. The distance at which the particle's
trajectory varied due to the presence of the wall was dependent on the impact Stokes
number. The particle surface roughness was found to affect the repeatability of some
measurements, especially for low impact velocities.