Vortex ring evolution and wall interaction in polymer solutions

Abstract

Addition of small quantity of polymer to a turbulent flow is shown to reduce the drag drastically. This phenomena (also known as Tom’s effect) is studied very rigorously, because of industrial applications and also as a tool to understand the physics behind fluid turbulence. In recent years it is discovered that addition of polymers can change the flow behavior in many spectacular ways: It can either stabilize a flow or can cause instability on its own, either reduce the drag or cause turbulence thereby increasing drag etc. Since polymers interact with the flow in a very complex way, it is very necessary to study the phenomena in a systematic way, by first considering only the simple flows. One main reason for not clearly understanding the polymer drag reduction is that, most studies done so far are in turbulent flows, which by itself is not clearly understood yet. Another important reason being the difficulty in characterizing the dilute polymer solution properties. Hence, we have chosen a simplistic version of this complex problem, i.e vortex ring in polymer solutions. Turbulent flow consists of eddies, which interact with polymers in different ways depending upon the time and length scales involved. A simplest model for such eddies is the vortex ring, which is easy to generate experimentally and is well understood. Hence, studying vortex rings in polymer solution should bring us one step closer to understand the physics behind polymer drag reduction.