Computation of a drastic flow pattern change in an annular swirling jet caused by a small decrease in inlet swirl

Vanierschot, Maarten; Bulck, Eric Van den

doi:10.1002/fld.1835

Cited by 8 publications

(6 citation statements)

References 10 publications

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“…Mullyadzhanov et al [30] presents a coherent literature review of the topic with LES results showing the hysteresis of the transition phenomenon with some conclusions on the differences between hot and cold regimes. Vanierschot and Van den Bulck [31,32] describe different flow patterns produced by these configurations emphasizing some of the features during the transition process. They focus on the hysteresis of the phenomenon.…”

Section: Introductionmentioning

confidence: 99%

Hydrodynamics During the Transient Evolution of Open Jet Flows from/to Wall Attached Jets

Valera‐Medina

Baej

2016

Flow Turbulence Combust

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Swirl stabilized flows are the most widely deployed technology used to stabilize gas turbine combustion systems. However, there are some coherent structures that appear in these flows close to the nozzle whose occurrence and stability are still poorly understood during transition. The external recirculation zone and the Precessing Vortex Core to/from the Coanda effect are some of them. Thus, in this paper the transition of an Open Jet FlowMedium Swirl flow pattern to/from a Coanda jet flow is studied using various geometries at a fixed Swirl number. Phase Locked Stereo Particle Image Velocimetry and High Speed Photography experiments were conducted to determine fundamental characteristics of the phenomenon. It was observed that the coherent structures in the field experience a complete annihilation during transition, with no dependency between the structures formed in each of the flow states. Moreover, transition occurs at a particular normalized step size whilst some acoustic shifts in the frequencies of the system were noticed, a phenomenon related to the strength of the vortical structures and vortices convection. It is concluded that a transient, precessing, Coanda Vortex Breakdown is formed, changing flow dynamics. The structure progresses to a less coherent Trapped Vortex between the two states. During the phenomenon there are different interactions between structures such as the Central Recirculation Zone, the High Momentum Flow Region and the Precessing Vortex Core that were also documented.

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Section: Introductionmentioning

confidence: 99%

Hydrodynamics During the Transient Evolution of Open Jet Flows from/to Wall Attached Jets

Valera‐Medina

Baej

2016

Flow Turbulence Combust

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“…2016). In line with an analysis by Vanierschot & van den Bulck (2009), Douglas et al. (2021) argued that these transitions occurred due to an exchange of dominance between low-pressure regions in the CRZ and ORZ.…”

Section: Introductionmentioning

confidence: 68%

“…An important detail of these studies was the characterisation of bistable central jet (CJ) and wall jet (WJ) states reminiscent of the hysteresis behaviour observed previously in annular swirling jets (Vanierschot & van den Bulck 2007;Ogus et al 2016). In line with an analysis by Vanierschot & van den Bulck (2009), Douglas et al (2021) argued that these transitions occurred due to an exchange of dominance between low-pressure regions in the CRZ and ORZ. However, these papers did not analyse the mechanics of this process in detail, and did not explore how the characteristics of the post-breakdown transition could be influenced by the axial wall's position or by the inclusion of a radial wall.…”

Section: Introductionmentioning

confidence: 72%

“…As mentioned in the Introduction, the bistable behaviour between CJ and WJ solutions observed in figure 2 is distinct from the basic vortex breakdown phenomenon. Indeed, Vanierschot & van den Bulck (2009) have explored such bistable behaviour and outlined some of the physical mechanisms at play as the flow transitions between states. Earlier work by the lead author has also shown that such bistable behaviour results from an exchange of dominance between low-pressure regions located within the CRZ and the ORZ based on analysis of the critical eigenmodes associated with the saddle–node bifurcations (Douglas et al.…”

Section: Resultsmentioning

confidence: 99%

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Confinement effects in laminar swirling jets

Douglas

Lesshafft

2022

J. Fluid Mech.

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This paper explores the effect of axial and radial confinement on the flow topology of laminar swirling jets. Its objective is to provide a unifying perspective toward swirling jet mechanics that connects earlier reports across a variety of confined and unconfined flow situations, and over a range of swirl ratio $S$ values. The analysis focuses separately on the influence of the jet's injection depth $L$ in a radially unconfined flow and of the chamber diameter $C$ in radially confined jets. In the former case, it shows that axial confinement influences strongly the jet's behaviour when $L$ is small, allowing bistable steady states: a central jet (CJ) solution with or without a small central recirculation zone (CRZ), and a wall jet (WJ) solution with a wide-open CRZ spreading along the reservoir's edge. Similar behaviour is identified for radially confined jets, where bistable CJ and WJ states appear over a range of moderate $C$ values, and the WJ state adopts a conical CRZ. In either case, the WJ solution appears or disappears via saddle–node bifurcations when the confinement is made sufficiently strong or weak, respectively. This dynamics is attributed to an exchange of dominance between central and outer low-pressure regions as the flow transitions from CJ to WJ, or vice versa. The findings demonstrate that the hysteresis associated widely with swirling jets is controlled not just by vortex breakdown, but also by confinement through the Coandă effect. Such confinement is found to alter significantly the state-space structure even when the walls are far from the nozzle.

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“…Comparison of Figs. 15 and 16 with the behavior of the OJF-HS with decreasing swirl, either a stationary decrease 11 or a sudden decrease, 23 shows that the physical mechanism that governs the transition is the increase in L CRZ and this mechanism is the same for both control methods. In the OJF, the increase in L CRZ is done by removing the cross injection, in the OJF-HS by decreasing the swirl.…”

Section: B Transient Flow Fieldsmentioning

confidence: 91%

A new method for annular jet control based on cross-flow injection

2009

Self Cite

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We propose a new method for controlling the outflow of a fully turbulent annular jet based on the cross-flow injection of secondary jets. Details are provided on an in-house designed nozzle with a specific geometry that causes an attachment of the annular jet to the nozzle cone when cross-flow injection is applied. When this cross injection is suddenly taken away, the nozzle attached jet evolves toward a stable wall jet. Time-resolved stereo particle image velocimetry measurements are used to characterize the three different flow patterns ͑annular, nozzle attached, and wall jet͒ and the aim of this investigation is to gain a deeper understanding into the physics of the transition from the nozzle attached jet to the wall jet.

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Computation of a drastic flow pattern change in an annular swirling jet caused by a small decrease in inlet swirl

Cited by 8 publications

References 10 publications

Hydrodynamics During the Transient Evolution of Open Jet Flows from/to Wall Attached Jets

Hydrodynamics During the Transient Evolution of Open Jet Flows from/to Wall Attached Jets

Confinement effects in laminar swirling jets

A new method for annular jet control based on cross-flow injection

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