Drag Reduction Caused by the Injection of Polymer Solutions into a Pipe Flow

Abstract

The mechanism of drag reduction caused by injection of concentrated polymer solutions into a turbulent pipe fllow was investigated by a tracer particle method, and the results were compared with those obtained by the previous LDV measurements.
The conclusions obtained in this study are summarized as follows;
(1) In a middle range of concentration of polymer, the multi-fine polymer threads (“MPT”) are mainly contained in the high speed large eddies of pipe flow. Both the radial fluctuation and the Reynolds stress for injected polymer threads are significantly suppressed, even at the center of pipe.
(2) For the injection of a high concentration polymer solution, a single polymer thread (“SPT”) is relatively stable, and does not divide into fine threads. The highly viscoelastic polymer thread flowing mainly at the center of pipe is non-turbulent but shows a wave-like motion. The injected polymer thread has a rather uniform velocity which is lower than the medium (water) velocity at the center. A significant suppression of the radial fluctuation was observed. The Reynolds stress shows almost the same distribution as that of a Newtonian fluid flow in the relatively wide central region but reduces strongly near the wall.
It was suggested that the wall turbulence structure could be controlled by suppressing the large eddy motion in the turbulent core region.