Experimental results are reported on hydrodynamic interactions between a solid plate with a spherical particle attached to it and a rigid sphere moving parallel to the plate. Trajectories and velocities of the moving sphere were determined by taking single-frame multiple-image photographs using stroboscopic light.
Sphere—sphere hydrodynamic interactions were detectable on the background of plate—sphere interactions for initial dimensionless sphere—wall separations Z0 < 4.9. The sphere trajectories were found to be symmetrical for, Z0 ≥ 2.3 and asymmetrical otherwise. For asymmetrical trajectories the sphere velocity was larger after the encounter than prior to it. It was concluded that surface roughness of the spheres was responsible for the observed deviations from symmetry.
Numerical calculations were performed to obtain sphere trajectories and velocities. The calculations agree with the experimental data for dimensionless distances between sphere centres r > 2.5. For r < 2.5 the numerical results were in fair agreement with the data when Z0 [gsim ] 2.9. For smaller Z0, theoretical predictions were inaccurate.