Author(s): B.B. Willetts; K.F. Naddeh
Abstract: A 20 mm diameter smooth sphere was held in a flow of oil by means of a device sensitive to the lift force exerted on the sphere. Lift force variations with gap ratio are reported for three approach velocity distributions, all at values of duct Reynolds number less than 1200, and at sphere Reynolds Number between 43 and 250. At gap ratios between 2 and 4 the lift force corresponds reasonably well with the prediction of Saffman [1, 2] for much lower Reynolds number. For smaller gaps, the flow through the gap between sphere and wall is dominant and the lift force direction is reversed. Transient lift forces are found when the sphere is in mid-duct, despite the laminar character of the approach flow. They are thought to be linked to the elongation of vortex elements shed from discrete arcs of the separation line and the effect of this elongation on conditions in the wake. Limited relevance is postulated to the motion of sand grains transported by water and air, but only in the absence of spin which would profoundly affect the flow patterns which underly the forces reported here.