Drag reduction by polymer addition

Abstract

The reduction of flow friction drag through polymer addition, a phenomenon first subjected to systematic study by Toms (1948) (with those name it is commonly associated) together with Oldroyd (1948), but of which the first documented discovery is due to Mysels (1949), has been the subject of very extensive research during the last decade. However, despite the combined efforts of specialists from many different fields, no satisfactory explanation of the phenomenon has as yet been found. Drag reduction has been observed with a large number of additive-fluid combinations (a few of which are shown in Fig. 1), the most effective ones being high-molecular-weight linear polymers (such as polyethyleneoxide) in water. There are clear experimental indications that drag reduction is associated with a modification of the turbulence structure, and this is most remarkable in view of the permanence and statistical stability exhibited by ordinary Newtonian shear flow turbulence. Therefore, the phenomenon of drag reduction becomes of interest not only because of the promising technical applications it offers but just as much for fundamental fluid mechanical reasons. Through the unravelling of the mechanism underlying the phenomenon one should not only improve the prospects of finding more efficient and perhaps completely novel methods of turbulence control, but should also hope to gain a substantially deepened understanding of the fundamental nature of turbulence as well.