Hysteresis and turbulent vortex breakdown in transitional swirling jets

Moise, P and Mathew, J (2021) Hysteresis and turbulent vortex breakdown in transitional swirling jets. In: Journal of Fluid Mechanics, 915 .

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Abstract

Vortex breakdown (VB) in unconfined swirling jets occurs as either a bubble form of vortex breakdown (BVB) or a conical form of vortex breakdown (CVB). This computational study examines flow features of these forms for a Reynolds number at which VB is accompanied by a transition to turbulence (, based on inflow jet radius and centreline velocity). Large eddy simulations were performed with the inflow condition as the Maxworthy profile which models a laminar, axisymmetric swirling jet, and the effect of varying inflow swirl strength was investigated. BVB was observed at lower swirl strengths than those at which CVB occurs. With increasing swirl, the regular and wide-open types of CVB occur. Spiral coherent structures that develop in the flow were examined using spectral proper orthogonal decomposition. Further, by means of hysteresis studies, it is established that the turbulent BVB and regular CVB are bistable forms. Similarly, it is shown that the two types of CVB are also bistable. The difference in recirculation zone (RZ) sizes between the turbulent BVB and regular CVB is greatly reduced when compared to the laminar counterparts. This is postulated as a reason for misidentification of CVB (RZ approximately conical in shape) as BVB (spheroidal RZ) in some previous studies. The present study highlights the distinct features of turbulent BVB and CVB, which can potentially be used towards improving designs of swirl-stabilized combustors. © The Author(s), 2021. Published by Cambridge University Press.

Item Type:	Journal Article
Publication:	Journal of Fluid Mechanics
Publisher:	Cambridge University Press
Additional Information:	The copyright for this article belongs to Cambridge University Press
Keywords:	Hysteresis; Large eddy simulation; Reynolds number; Vortex flow, Coherent structure; Computational studies; Improving designs; Inflow conditions; Proper orthogonal decompositions; Recirculation zones; Transition to turbulence; Turbulent vortices, Rhenium compounds, hysteresis; jet; laminar-turbulent transition; large eddy simulation; Reynolds number; vortex
Department/Centre:	Division of Mechanical Sciences > Aerospace Engineering(Formerly Aeronautical Engineering)
Date Deposited:	04 Jul 2021 05:42
Last Modified:	04 Jul 2021 05:42
URI:	http://eprints.iisc.ac.in/id/eprint/68735

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