Characterization of jets issuing from circular nozzles with A-shaped notch lip-modifications

Abstract

Jets exhausting from circular nozzles lip-modified with A-shaped notches of different relative sharpness were studied using digital particle image velocimetry. Results show that along the trough-to-trough planes, in addition to large-scale shear layer vortices, small-scale secondary vortex structures are formed close to the jet centrelines. Along the peak-to-peak planes, small-scale streamwise-aligned vortex structures are formed along the jet peripheral instead, while shear layer vortices move towards the jet centrelines. Flow stresses are also generally higher along peak-to-peak planes than along trough-to-trough planes. Half jet-width and momentum thickness profiles for the lip-modified nozzles are significantly wider than those for a non-lip-modified reference nozzle. Furthermore, half jet-width profiles taken along the peak-to-peak and trough-to-trough planes demonstrate trends and crossover locations, which are reminiscent of noncircular jet axis-switching behaviour. Lastly, increasing the nozzle-relative sharpness here accentuates the vortex dynamics but not necessarily leading to further favourable flow behaviour.

Keywords:

• free shear layers
• vortex dynamics
• jet mixing
• indeterminate-origin jets
• particle image velocimetry

Acknowledgements

The authors acknowledge the support by UK-EPSRC for the second author under the Doctoral Training Account scholarship and the support by the University of Liverpool Research Development Fund for the project.