An experimental study of hydrodynamic behavior of rotating spherical particles in a quiescent viscous fluid

The motion of solids in a viscous fluid with nonlinear complex behavior has important applications in different industries and engineering sciences. This work experimentally investigated the free-fall behavior of rotating and non-rotating spherical particles in a viscous fluid. The effects of physical parameters, including particle size, particle density, fluid viscosity, and rotational velocity, on the terminal velocity of the falling spherical particles were examined. A high-speed camera was employed to capture the phenomena and study the free-fall behavior of the spherical solid particles in a viscous fluid. The studied spherical particles had five different densities of 2800, 7800, 7900, 8660, and 8960 kg/m 3 and three varying dimensions of 4, 5, and 6 mm. To explore the effect of fluid viscosity on the terminal velocity of particles, two types of fluids with the viscosities of 0.012 and 0.014 Pa.s were used. The initial rotational velocities were 0, 600, 900, and 1200 rpm for the falling particles. The obtained results revealed that increases in the particle diameter, density, and rotational velocity, along with a decrease in fluid viscosity, accelerated the terminal velocity and shortened the time of reaching this velocity. Furthermore, an increase in the Reynolds number gave rise to a decrease in the lift coefficient. On the other hand, the accelerated dimensionless rotational velocity increased the lift coefficient.