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Cross-sectional reshaping of perturbed/unperturbed rectangular jets

Cross-sectional reshaping of perturbed/unperturbed rectangular jets This study aims to investigate the cross-sectional reshaping in transitioning/starting rectangular jets of aspect ratio 2 under various inlet perturbation conditions at the Reynolds number of Re = UDh/v = 17,750.Design/methodology/approachLarge eddy simulation results compared with the phase-locked particle image velocimetry data exhibit the cross-sectional jet deformations from rectangular to rounder shapes. Inflow velocity oscillations are introduced at the fundamental frequency associated with the Kelvin–Helmholtz instability characterized by the spectral analysis of the hotwire data and the linear stability predictions.FindingsThe initially rectangular cross-section of the jet reshapes into the rounder geometries with increased downstream distance while the edges of the jet become distorted due to the shear layer instability more significantly observed near the high curvature corners. The different expansion rates in the longer and shorter edges of the jet and the consequent cross-sectional reshaping are found to be sensitive to small levels of random inlet perturbations. In addition, introducing controlled sinusoidal oscillations results in the formation of more organized trailing shear layer where the stronger vortex rings go through the curvature-induced deformations.Originality/valueSpatio-temporal study of vortex dynamics in transitioning rectangular jets reveals important information about the effect of the controlled jet forcing on local entrainment. Dynamics of the leading vortex dominates the entrainment in transitioning jets which are commonly used in practical applications. Near-field entrainment is also promoted proportional to the amplitude of the controlled inlet oscillations within the trailing vortex rings. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Numerical Methods for Heat & Fluid Flow Emerald Publishing

Cross-sectional reshaping of perturbed/unperturbed rectangular jets

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Publisher
Emerald Publishing
Copyright
© Emerald Publishing Limited
ISSN
0961-5539
DOI
10.1108/hff-09-2018-0479
Publisher site
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Abstract

This study aims to investigate the cross-sectional reshaping in transitioning/starting rectangular jets of aspect ratio 2 under various inlet perturbation conditions at the Reynolds number of Re = UDh/v = 17,750.Design/methodology/approachLarge eddy simulation results compared with the phase-locked particle image velocimetry data exhibit the cross-sectional jet deformations from rectangular to rounder shapes. Inflow velocity oscillations are introduced at the fundamental frequency associated with the Kelvin–Helmholtz instability characterized by the spectral analysis of the hotwire data and the linear stability predictions.FindingsThe initially rectangular cross-section of the jet reshapes into the rounder geometries with increased downstream distance while the edges of the jet become distorted due to the shear layer instability more significantly observed near the high curvature corners. The different expansion rates in the longer and shorter edges of the jet and the consequent cross-sectional reshaping are found to be sensitive to small levels of random inlet perturbations. In addition, introducing controlled sinusoidal oscillations results in the formation of more organized trailing shear layer where the stronger vortex rings go through the curvature-induced deformations.Originality/valueSpatio-temporal study of vortex dynamics in transitioning rectangular jets reveals important information about the effect of the controlled jet forcing on local entrainment. Dynamics of the leading vortex dominates the entrainment in transitioning jets which are commonly used in practical applications. Near-field entrainment is also promoted proportional to the amplitude of the controlled inlet oscillations within the trailing vortex rings.

Journal

International Journal of Numerical Methods for Heat & Fluid Flow – Emerald Publishing

Published: Aug 30, 2019

Keywords: Flow control; Entrainment; Rectangular jets; Vortex rings

References

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