Investigation of interactions between a sphere wake and free surface

Abstract

This paper presents flow-structure interaction between a sphere wake and a free water surface for different submerged elevations in an open water channel for Reynolds numbers in the range of 2.5x10(3) <= Re <= 1x10(4) based on the diameter of the sphere. Particle Image Velocimetry (PIV) and dye visualization techniques were performed to demonstrate flow patterns such as instantaneous and time-averaged velocity field, streamline topology, vortices, velocity contours. The sphere was fixed at various submerged locations from the piercing the free surface case to the two sphere diameters beneath the free surface in the range of 0.25 <= h/D <= 3.0. Here, submerged ratio was defined as ratio of bottom shoulder of the sphere from the free surface to the sphere diameter. Depending on the sphere locations, characteristics of wake region exhibit three different flow phenomena. These are classified as; a restricted wake region between the free-surface and uniform flow stream for the submerged ratios of 0.25 <= h/D <= 1.0, unsymmetrical flow patterns due to the free surface effect for the submerged ratios of 1.25 <= h/D <= 2.0 and symmetrical flow structures for the submerged ratios of 2.5 <= h/D <= 3.0 More detailed results for the aforementioned flow structures from the point of flow physics were comparatively presented and interpreted.