A generalized relationship for swirl decay in laminar pipe flow

Swirling flow is of great importance in heat and mass transfer enhancements and in flow measurements. In this study, laminar swirling flow in a straight pipe was considered. Steady three-dimensional axisymmetric Navier-Stokes equations were solved numerically using a control volume approach. The swirl number distribution along the pipe length was computed. It was found that the swirl number at any location along the pipe length depends on the swirl number at inlet, the flow Reynolds number, the distance from the pipe inlet, the pipe diameter and the nature of the inlet swirl. A generalized relationship for swirl decay as a function of these parameters was then obtained by curve-fitting technique.