CREEPING SPHERE MOTION IN HERSCHEL-BULKLEY FLUIDS - FLOW-FIELD AND DRAG

The results of a comprehensive experimental study on the creeping sphe re motion in Herschel-Bulkley model fluids are reported and discussed in this paper. A series of aqueous solutions of different grades of Ca rbopol resin have been used to encompass wide ranges of theological mo del parameters. In particular, the size and shape of the sheared cavit y surrounding a moving sphere and the drag behaviour have been investi gated in this study. A laser-speckle tracer method was used to obtain information on the structure of the flow field about a sphere which, i n turn, shows the size and shape of the underformed regions in the flo w domain. The measured terminal velocity data together with the physic al properties and dimensions have been used to deduce the values of dr ag coefficient as a function of the pertinent dimensionless groups. Th e paper is concluded by presenting extensive comparisons, of both shea red cavity characteristics and drag behaviour, between the present res ults and the literature correlations and/or data.