Vortex breakdown: a review

Lucca-Negro, O.; O'Doherty, Timothy

doi:10.1016/s0360-1285(00)00022-8

Cited by 679 publications

(325 citation statements)

References 66 publications

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“…The existence of such a lean and cold zone leads to the formation of a PVC [4][5][6][7][8]. This PVC only occurs in the 2% case and precesses at 408Hz.…”

Section: Resultsmentioning

confidence: 99%

“…A key zone of the chamber controlling instabilities is the burner outlet section where swirl is very intense and must provide flame stabilisation. In these regions, the natural unstable modes of swirling flows (Precessing Vortex Cores or PVCs [4][5][6][7][8]) can interact with stabilisation and lift-off phenomena [9][10][11][12] to produce undesired oscillations.…”

Section: Introductionmentioning

confidence: 99%

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Large eddy simulation of piloting effects on turbulent swirling flames

Sengissen

Giauque

Staffelbach

et al. 2007

Proceedings of the Combustion Institute

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Pilot flames, created by additional injectors of pure fuel, are often used in turbulent burners to enhance flame stabilisation and reduce combustion instabilities. The exact mechanisms through which these additional rich zones modify the flame anchoring location and the combustion dynamics are often difficult to identify, especially when they include unsteady hydrodynamic motion. This study presents Large Eddy Simulations (LES) of the reacting flow within a large-scale gas turbine burner for two different cases of piloting, where either 2 or 6 percent of the total methane used in the burner is injected through additional pilot flame lines. For each case, LES shows how the pilot fuel injection affects both flame stabilisation and flame stability. The 6 percent case leads to a stable flame and limited hydrodynamic perturbations in the initial flame zone. The 2 percent case is less stable, with a small-lift-off of the flame and a Precessing Vortex Core (PVC) in the cold stabilisation zone. This PVC traps some of the lean cold gases issuing from the pilot passage stream, changes the flame stabilisation point and induces instability.

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“…The existence of such a lean and cold zone leads to the formation of a PVC [4][5][6][7][8]. This PVC only occurs in the 2% case and precesses at 408Hz.…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Large eddy simulation of piloting effects on turbulent swirling flames

Sengissen

Giauque

Staffelbach

et al. 2007

Proceedings of the Combustion Institute

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“…They feature several types of vortex breakdown and can exhibit bifurcation phenomena where different states can co-exist and the flow can jump spontaneously from one to another [1,2]. Bifurcations of flames in configurations which are close to real gas turbine chambers have not been investigated so far even though engineers report that they observe these mechanisms and that there is a link between flame states and thermoacoustic instabilities: when the flame changes from one state to another, its acoustic stability characteristics also change.…”

Section: Introductionmentioning

confidence: 99%

Bistable swirled flames and influence on flame transfer functions

Hermeth

Staffelbach

Gicquel

et al. 2014

Combustion and Flame

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Large Eddy Simulations (LES) are used to study a lean swirl-stabilized gas turbine burner where the flow exhibits two stable states. In the first one, the flame is attached to the central bluff body upstream of the central recirculation zone which contains burnt gases. In the second one the flame is detached from the central bluff body downecirculation zone which is filled by cold unburnt gases and dominated by a strong Precessing Vortex Core (PVC). The existence of these two states has an important effect on the dynamic response of the flame (FTF): both gain and phase of the FTF change significantly in the detached case compared to the attached one, suggesting that the stability of the machine to thermoacoustic oscillations will differ, depending on the flame state. Bifurcation diagrams show that the detached flame cannot be brought back to an attached position with an increased fuel flow rate, but it can be re-attached by forcing it at high amplitudes. The attached flame however, behaves inversely: it can be brought back to the detached position by both decreasing or increasing the pilot mass flow rate, but it remains attached at all forcing amplitudes. IntroductionSwirling flows are commonly used to help flame stabilization in gas turbine combustion chambers. They feature several types of vortex breakdown and can exhibit bifurcation phenomena where different states can co-exist and the flow can jump spontaneously from one to another [1,2]. Bifurcations of flames in configurations which are close to real gas turbine chambers have not been investigated so far even though engineers report that they observe these mechanisms and that there is a link between flame states and thermoacoustic instabilities: when the flame changes from one state to another, its acoustic stability characteristics also change.Two dynamic phenomena are usually observed in swirled combustion chambers: (1) a helical flow instability, the so-called precessing vortex core (PVC) and (2) thermo-acoustic instabilites.The PVC is an hydrodynamic instability in swirling flows [3].I t is a large scale structure characterized by a regular rotation of a spiral structure around the geometrical axis of the combustion chamber. It can occur at high Reynolds and swirl number flows [4][5][6][7][8][9][10] and its precession frequency is controlled by the rotation rate of the swirled flow [3]. Several studies show that combustion can suppress the PVC [6,7,11], but other cases also show PVCs which are present in reacting flows [12][13][14][15]. The interaction of PVC with flames has been analyzed for example by Stöhr et al.[16]: they found the PVC to enhance mixing and to increase the flame surface. This was associated to structures in the inner shear layer, whereas Moeck et al. [15] observed the outer shear layer to create most of the flame perturbations. Both researchers as well as Staffelbach [13] using LES evidenced a ''finger-like'' rotating structure at the flame foot around which the PVC is turning. Furthermore, asymmetric fluctuations of the he...

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“…The characteristic viscous length scale for swirling flows is properly represented by the Reynolds number based on the vortex-core diameter, if present [7]. However, most of the literature data refer to the Reynolds number based upon the burner diameter:…”

Section: Design and Operating Parameters Of Swirling-flow Combustorsmentioning

confidence: 99%

“…An early state-of-the-art of the experimental findings on swirling reacting flows and their modelling is provided in [6]. In [7] the authors analyse the types of vortex breakdown (which precedes the CRZ formation) and present the effect of inlet conditions and geometry on the structures of recirculation zones.…”

Section: Introductionmentioning

confidence: 99%

Effect of the Reynolds number and the basic design parameters on the isothermal flow field of low-swirl combustors

Gobbato

Masi

Cappelletti

et al. 2017

Experimental Thermal and Fluid Science

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Swirling flows through sudden expansions is a common solution adopted to stabilise the flame within combustion systems. Fuel-air mixing promoted by the swirling motion contributes also to complete the fuel oxidation and reduce pollutant emissions. (http://www.sciencedirect.com/science/article/pii/S0894177717300304) 2 extended considering original measurements performed by the authors on a laboratory combustor.The comparison shows that the flow field of low-swirl combustors is mainly affected by the Reynolds number. Among the design parameters considered, the expansion ratio is the most significant. In particular, the former controls the radial position of the velocity peak whereas the latter influences the axial decay of velocity within the jet core.

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Vortex breakdown: a review

Cited by 679 publications

References 66 publications

Large eddy simulation of piloting effects on turbulent swirling flames

Large eddy simulation of piloting effects on turbulent swirling flames

Bistable swirled flames and influence on flame transfer functions

Effect of the Reynolds number and the basic design parameters on the isothermal flow field of low-swirl combustors

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