Hysteresis in flow patterns in annular swirling jets

This study investigates the influence of swirl on the mean cold flowfield of an annular jet with a stepped-conical expansion. Both the axial and azimuthal velocity components are measured using a two component Laser Doppler Anemometry system in forward scattering mode. A detailed description of the radial profiles of both mean axial and azimuthal velocity as well as three components of the Reynolds stress are given. Four different jets are identified as a function of the swirl number: ‘Closed Jet Flow’, ‘Open Jet Flow Low Swirl’, ‘Open Jet Flow High Swirl’ and ‘Coanda Jet Flow’. These flow patterns change with varying swirl number and there exists hysteresis when increasing and subsequently decreasing the swirl. Also a method for jet identification based upon pressure measurements is presented to replace the time consuming LDA measurements.