Characteristics of Turbulent Swirling Flow in a Straight Pipe

Change in Angular Momentum with Swirl Decay

Abstract

The swirl effects on the angular momentum distribution of turbulent swirling flow in a straight pipe are described. When the swirl strength increases, the axial velocity decreases in the central region and its distribution becomes constant in the annular region of the pipe, except in the boundary layer adjacent to the pipe wall. Tangential velocity induces the formation of a combined vortex similar to the Rankine vortex which is a solid vortex in the central domain and a free vortex in the annular region of the pipe. Although factors that affect flow, such as the contours of the swirling angle, axial and tangential velocities and fluctuation velocity, have been discussed previously by the authors, their analyses have not yet been conducted. The local angular momentum at radius, r, in the pipe is employed in this study. As a result, the local angular momentum downstream does not change in the central region but decreases in the annular region of the pipe. It is suggested that most of the swirl decay in a straight pipe depends on the viscous forces that occur either between fluids or between a fluid and the pipe wall in the annular region of the pipe.