Abstract
In order to investigate the relation between flow structure and free sphere's motion in the divergent channel expanding upwards, observation of the sphere's motion and PIV analysis of the flow were carried out. The sphere motion could be classified into two categories; pattern (a), the sphere lifts toward the flow direction with rotation; and pattern (b), the sphere lifts with rotation also revolution along the channel wall. Pattern (a) appears when the Reynolds number of the flow around the sphere is larger than a certain value given by the sphere weight and size, and vice versa. A vortex ring is generated in the sphere wake and it horizontally stays in the case of Pattern (a). The vortex ring, however, cants to the sphere side and revolves with the sphere in the case of Pattern (b).
