Crossflow Influence on Transverse Jet Shear Layer Instabilities: Experimental Studies

Journal of Fluid Mechanics, 2008

The dominant non-dimensional parameter for isodensity transverse jet flow is the mean jet-to-crossflow velocity ratio, R. In Part 1 (Megerian et al., J. Fluid Mech., vol. 593, 2007, p. 93), experimental results are presented for the behaviour of transverse-jet near-field shear-layer instabilities for velocity ratios in the range 1 < R 10. The nominally axisymmetric mode is found to be the most unstable mode in the transverse-jet shear-layer near-field region, upstream of the end of the potential core. The overall agreement of theoretical and experimental results suggests that convective instability occurs in the transverse-jet shear layer for jet-to-crossflow velocity ratios above 4, and that the instability is strengthened as R is decreased.

2009

Shear layer instabilities associated with the gaseous, isodensity jet in crossflow have been explored in detail in recent experimentsfootnotetextMegerian, et al., JFM, 593, pp. 93-129, 2007, indicating that the jet shear layer is globally unstable when the jet-to-crossflow velocity ratio, R, is less than 3.2 for a flush injected jet. Low density jets in quiescent surroundings are also known to become globally unstable for jet-to-ambient density ratios below approximately 0.6-0.7. It is thus of interest to explore the nature of changes in the character of shear layer instabilities for the low density jet in crossflow, with special focus on the influence of jet-to-crossflow momentum flux ratios at which instabilities are altered. A specially designed mixing device is utilized for exploration of helium and nitrogen jet mixtures. Calibration of the mixing device is accomplished using an acoustic waveguide capable of exploring alterations of standing wave frequencies with different gas mixtures. A range of flow conditions are explored, and alterations in the jet's spectral character suggesting transition to absolute instability are quantified.

Journal of Fluid Mechanics, 2011

2021

This experimental study explores and quantifies mixing characteristics associated with a gaseous round jet injected perpendicularly into cross-flow for a range of flow and injection conditions. The study utilizes acetone planar laser-induced fluorescence imaging to determine mixing metrics in both centreplane and cross-sectional planes of the jet, for a range of jet-to-cross-flow momentum flux ratios (2 J 41), density ratios (0.35 S 1.0) and injector configurations (flush nozzle, flush pipe and elevated nozzle), all at a fixed jet Reynolds number of 1900. For the majority of conditions explored, there is a direct correspondence between the nature of the jet's upstream shear layer instabilities and structure, as documented in detail in Getsinger et al. (J. Fluid Mech., vol. 760, 2014, pp. 342–367), and the jet's mixing characteristics, consistent with diffusion-dominated processes, but with a few notable exceptions. When quantified as a function of distance along the jet trajectory, mixing metrics for jets in cross-flow with an absolutely unstable upstream shear layer and relatively symmetric counter-rotating vortex pair cross-sectional structure tend to show better local molecular mixing than for jets with convectively unstable upstream shear layers and generally asymmetric cross-sectional structures. Yet the spatial evolution of mixing with downstream distance can be greater for a few specific convectively unstable conditions, apparently associated with the initiation and nature of shear layer rollup as a trigger for improved mixing. A notable exception to these trends concerns conditions where the equidensity jet in cross-flow has an upstream shear layer that is already absolutely unstable, and the jet density is then reduced in comparison with that of the cross-flow. Here, density ratios below unity tend to mix less well than for equidensity conditions, demonstrated to result from differences in the nature of higher-density cross-flow entrainment into lower-density shear layer vortices.

Physical Review Fluids

AIAA Journal, 2010

AIAA Journal, 2019

Flow, Turbulence and Combustion, 2016

Human Rights Review, 2015