Criterion for the linear convective to absolute instability transition of a jet in crossflow: The countercurrent viscous and round mixing-layer analogy

Souza, Davi; Freitas, Rômulo Bessi; Alves, Leonardo Santos de Brito

doi:10.1103/physrevfluids.6.l041901

Cited by 4 publications

(3 citation statements)

References 28 publications

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“…Megerian et al [15] and Shoji et al [18] note a similar peaking of the dominant instability frequency at the transition point between a CU and AU JICF for a range of jet flow conditions, with and without acetone tracer. Both experiments by Shoji et al [18] and the LSA of Souza et al [26] indicate that the variability in frequencies associated with these dominant instabilities for lower J values may be traced to competing dynamics of an increase in the jet momentum thickness and a strengthening of a counter-current shear layer (CCSL)-like behavior at the USL as crossflow velocity U ∞ increases. The CCSL behavior originates from the small negative velocity component induced by the recirculation zone upstream of the leading edge of the jet as the crossflow velocity increases (decreasing J), explored in detail in Shoji et al [18].…”

Section: A Spectral Measurementsmentioning

confidence: 98%

“…There is also a change in the dominant instability frequency of the USL with changes in the constituent species. Separate linear stability analysis (LSA) by Souza et al [26] demonstrates that the instability characteristics of the JICF, and the critical transition from a CU USL to an AU USL, are dependent on the momentum thickness of the issuing jet, and hence viscous effects and finite Reynolds number, in addition to jet curvature effects. Because the USL instability characteristics for a larger flush nozzle (D = 7.59mm) utilized in the present study have not been investigated beyond the preliminary studies in early jet control experiments [32,33], we seek a more detailed exploration of such characteristics.…”

Section: A Spectral Measurementsmentioning

confidence: 99%

“…Given the complexities and interdependencies associated with the system of vortical structures for the JICF, a number of recent studies have investigated the dynamics of the flowfield experimentally [15][16][17][18], numerically [19][20][21][22][23], and theoretically [24][25][26]. In many of these studies there is special emphasis placed upon the upstream and downstream shear layer instabilities.…”

Section: Introductionmentioning

confidence: 99%

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Effects of controlled vortex generation and interactions in transverse jets

et al. 2022

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This experimental study examined the effects of controlled vortex generation and interactions created by axisymmetric excitation of a transverse jet, with a focus on the structural and mixing characteristics of the flow. The excitation consisted of a novel double-pulse forcing waveform applied to the jet, where two distinct temporal square wave pulses were prescribed during a single forcing period. The two distinct pulses produced vortex rings of different strength and celerity, the strategic selection of which promoted vortex ring interactions or collisions in the nearfield to varying degrees. Jet flow conditions corresponding to a transitionally convectively/absolutely unstable upstream shear layer (USL) in the absence of forcing, at a jet-to-crossflow momentum flux ratio of J = 10, and to an absolutely unstable USL at J = 7, were explored for a jet Reynolds number of 1800. Acetone planar laser-induced fluorescence (PLIF) imaging was utilized to quantify the influence of different prescribed temporal waveforms. All forcing conditions enhanced the spread, penetration, and molecular mixing of the jet as compared to the unforced jet, though to differing degrees. Interestingly, when the jet was convectively unstable, forcing which promoted vortex collisions provided the greatest enhancement in molecular mixing, whereas the absolutely unstable jet produced the greatest enhancement in mixing when the vortex rings did not interact, with important implications for optimized jet control.

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Section: A Spectral Measurementsmentioning

confidence: 98%

Section: A Spectral Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of controlled vortex generation and interactions in transverse jets

et al. 2022

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Dynamics of elevated dodecane jets in crossflow at supercritical pressure

Ding,

Li,

Wang

2024

Physics of Fluids

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In advanced aero-engines, kerosene is often transversely injected into the combustor at supercritical pressure, where the shorter jet penetration depth may result in poor mixing and the local hot spots near the combustor wall. Elevating the jet nozzle is proposed to remedy these issues, where the flowfield complexity increases as a result of the intricate interactions among the jet, crossflow, and stack wake. The distinct flow dynamics of elevated dodecane jets in crossflow (EJICF) at supercritical pressure are numerically investigated using large eddy simulation. The effects of various parameters, including ambient pressure, elevation stack thickness, and stack height are studied. The results reveal that, the jet-wake recirculation bubble is prominently evident at low supercritical pressure, attributed to the strong real-fluid effect resulting from significant density stratification in the jet's upstream shear layer. Analysis of streamline patterns and vorticity budgets underscores the role of the real-fluid effect in delaying the shift of the flow pattern from the transitional regime to the jet-dominated regime. Increasing stack thickness mitigates the impact of jet upshear effects and has the potential to eliminate the lock-in phenomena between jet wake and stack wake. A reduction in stack height leads to the diminishment of the stack wake vortex shedding. In contrast to conventional JICF, the EJICF configuration exhibits a heightened tendency for recirculation bubble formation in the jet wake region. An analysis of spatial mixing deficiencies demonstrates that incorporating an elevation stack with proper thickness and height can dramatically improve the jet-crossflow mixing efficiency.

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