Cross-stream behaviour and flow characteristics of hybrid inclined nozzle jets

Abstract

An experimental flow visualization and particle-image velocimetry (PIV) study was carried out on hybrid inclined nozzles to examine their near-field vortex dynamics and evaluate their impact upon the cross-stream flow characteristics. This study complements streamwise PIV measurements presented by New and Tsovolos (Flow Turbul. Combust., vol. 83, 2009, pp. 485–509) in understanding how inclined jets may be modified. Laser-induced fluorescence flow images reveal that regular pairings take place between vortex roll-ups formed under forced flow conditions and secondary vortex loops induced between them. The vortex loops appear to be similar to those observed by Webster and Longmire (Phys. Fluids, vol. 9, 1997, pp. 655–666) and Troolin and Longmire (Exp. Fluids, vol. 48, 2009, pp. 409–420) in vortex rings issuing from simple inclined nozzles. Flow interpretations based on these earlier studies are presented to explain the current observations. PIV results demonstrate the resilient formation of streamwise-aligned vortices along the inclined section, where a sharper inclined section results in later but eventually stronger formations. Their presence not only introduces asymmetries in the jet cross-sections but also alters the distributions and magnitudes of the cross-stream Reynolds stresses. Lastly, hybrid inclined nozzles produce different half jet widths and momentum thicknesses along different azimuthal locations, where inclined sections produce smaller half jet widths but significantly thicker momentum thicknesses, as compared to the flat sections. A sharper inclined section does not lead to significant deviations in these flow quantities and suggests that the resultant intensified near-field vortex interactions appear to affect the cross-stream quantities more significantly.

Keywords:

• inclined jets
• flow dynamics
• laser-induced fluorescence
• particle-image velocimetry

Acknowledgements

The support provided for the second author by the UK Engineering and Physical Science Research Council Doctoral Training Account, as well as support from the University of Liverpool Research Development Fund and Department of Engineering Research Support Budget for the research project, is gratefully acknowledged.