Experimental Investigation of the Hydrodynamic Interactions between a Sphere and a Large Spherical Obstacle

(Received 2 June 1994, received in final form 19 October 1994, accepted 24 October 1994)

Abstract
The hydrodynamic interactions between a spherical particle embedded in a very viscous fluid and a large close spherical obstacle are investigated experimentally. The displacement of the particle is followed by laser interferometry with a 100 nm resolution. The large obstacle is either convex, plane or concave. The experimental results for the drag coefficient on the particle are compared to the theoretical results written as three terms expansions for small gaps, viz. the result of Cox and Brenner (1967) for a plane obstacle, the result of Jeffrey (1982) and Jeffrey and Onishi (1984) for a convex obstacle and an extension of Cooley and O'Neill (1969) for a concave obstacle. Excellent agreement is found between the experimental and the theoretical results for all cases.