Experimental Study on Developing Flexible Tubes with Turbulent Drag Reduction Effects

Abstract

In order to probe into developing technology for pipe fluid transportation with drag reducing effects by using a flexible tube, an experimental study was performed on the effects of turbulent drag reduction by using sleeve-structured flexible tubes in the operating conditions that there are water and air with pressure to be almost equivalent to the pressure on inner wall surface, on external wall surface of the flexible tubes. The results are found as follow: the thinner the flexible tubes, the bigger the decrease rate of the friction coefficient is; compared the drag reduction rates in operating condition of pressure balancing air with those in operating condition of pressure balancing water, the drag reduction rates for former are bigger, at Re=17500, the drag reduction rates of the flexible tubes with thickness of 2mm, 3mm and 4mm, are about 12%, 10%, 9%. This would offer a new view for developing technology of efficient fluid transportation. It's very important to develop energy-saving and friction drag reduction technologies for resolving the contradiction among global sustainable development, energy's drying up and increasing energy consumption with population's growth and industry's rapid development. The fluid transportation via industrial pipeline is done essentially in turbulent flow patterns, so the turbulent friction drag reduction is an inevitable requirement for transporting fluid effectively. The turbulent friction drag reduction focus on changing the turbulent coherent structure in the boundary layer on solid wall to reduce the internal energy dissipation. The representative methods for reducing friction drag are as follow: adding polymer or surfactant into fluid based on the Toms' effects, riblet, large eddy brake up device and compliant wall. With regard to riblet, since reported by Walsh (1) first,