A Swirling Round Turbulent Jet: 1—Mean-Flow Measurements

A swirling jet of air is generated for this work by flow issuing from a rotating pipe into a reservoir of motionless air. At the pipe discharge, the flow is roughly a fully developed, turbulent pipe flow in solid-body rotation. Owing to the very rapid decay of the swirl, measurements are confined to a region extending from the pipe discharge out to a distance of 15 pipe diameters. Mean-velocity magnitudes and mean directions are the primary results; in addition, one turbulence intensity component is included. All velocities and intensities were measured with a constant-temperature hot-wire anemometer having a linearized response, and all mean values were determined by electronic integration. Contrasted with the nonswirling jet, the jet with swirl spreads at a larger angle, entrains reservoir fluid more rapidly, and consequently displays a more rapid reduction of mean-velocity and growth of turbulence intensity. In its gross features, at large distances from the orifice, the measured swirling jet agrees with the predictions of “weak-swirl” analyses.