Flow of dilute polymer solutions about circular cylinders

Abstract

Experiments on fully attached flows of aqueous solutions of Polyox WSR-301 and pure solvent (tap and distilled water) about circular cylinders were carried out in the range 5 × 104<Re< 3 × 105for the initial purpose of providing definitive experimental information on drag reduction with additives in external flows.During the course of the investigation, a critically degraded polymer solution was observed to cause, at a particularRe, an unforseen instability in the separation line, similar to that first observed by Brennen (1970 in fully developed cavity flows. This instability, which most easily manifest edit self in the form of an abrupt drag-force jump (here called a drag crisis) from a high subcritical to a low supercritical value, became the central issue in the investigation. Efforts to isolate the causes of this instability led to further experiments with suspensions of nearly neutrally buoyant spherical and non-spherical particles. The measurements have shown that fibres and polymer hasten transition, spherical particles do not appreciably affect the characteristics of the flow and that neither the spherical particles nor fibres give rise to a drag crisis.