THE RATE OF DECAY OF SWIRL IN TURBULENT PIPE-FLOW

An experimental study is performed for the development of the mean vel ocity field of swirling turbulent flows in straight pipes with a smoot h wall. Swirl intensities were selected in a range that can be expecte d to occur in large piping systems. Measurements were taken for two di fferent Reynolds numbers, and two widely different initial conditions. Although the swirl intensity can best be expressed by the axial flow of angular momentum, a representation by a single swirl angle seems to be satisfactory for the final decay process. While the difference bet ween the initial conditions persists during a considerable part of the decay process, the decay rates are not essentially different. The rat e of decay appears to vary with the Reynolds number in the same way as the friction factor does. (C) 1998 Elsevier Science Ltd. All rights r eserved.