Planar Liquid Sheet Breakup of Prefilming and Nonprefilming Atomizers at Elevated Pressures

Bhayaraju, Umesh; Hassa, Christoph

doi:10.1615/atomizspr.v19.i12.50

Cited by 32 publications

(25 citation statements)

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“…More recently, the investigation of prefilming airblast atomization with a varying ambient pressure was conducted by Batarseh (2008) on an annular swirling injector with Phase Doppler Anemometry (PDA) located, at the closest, at 3 mm downstream of the nozzle exit. The author varied the ambient pressure and the gas velocity to keep the mass flow rate constant, and observed a non monotonic evolution of the SMD when increasing the Bhayaraju & Hassa (2009) investigated prefilming airblast atomization at high pressure using a planar injector with PDA located, at the closest, 10 mm downstream the nozzle exit. The authors also reported a storage mechanims of the liquid at the prefilmer tip.…”

Section: Introductionmentioning

confidence: 99%

Influence of the ambient pressure on the liquid accumulation and on the primary spray in prefilming airblast atomization

Chaussonnet

Gepperth

Holz

et al. 2020

International Journal of Multiphase Flow

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The influence of the ambient pressure on the breakup process is investigated by means of PIV and shadowgraphy in the configuration of a planar prefilming airblast atomizer. The ambient pressure is varied from 1 to 8 bar. Other investigated parameters are the gas velocity and the film loading. From single-phase PIV measurements, it is found that the gas velocity in the vicinity of the prefilmer partly matches the analytical profile from the near-wake theory. The shadowgraphy images of the liquid phase directly downstream of the prefilmer allow to extract characteristic quantities of the liquid accumulation at the atomizing edge. Two different characteristic lengths, as well as the ligament velocity and a breakup frequency are determined. In addition, the droplets generated directly downstream of the liquid accumulation are captured. Hence, the spray Sauter Mean Diameter (SMD) and the mean droplet velocity are given for each operating point. A scaling law of these quantities with regard to ambient pressure is derived. A correlation is observed between the characteristic length of the accumulation and the SMD, thus promoting the idea that the liquid accumulation determines the primary spray characteristics. An threshold to distinguish the zones between primary and secondary breakup is proposed based on an objective criterion. It is also shown that taking non-spherical droplets into account significantly modifies the shape of the dropsize distribution, thus stressing the need to use shadowgraphy when investigating primary breakup. The ambient pressure and the velocity are varied accordingly to keep the aerodynamic stress ρ g U 2 g constant. This leads to almost identical liquid accumulation and spray characteristics. Hence, it is confirmed that the aerodynamic stress is a more appropriate parameter than the gas velocity or the ambient pressure to characterize prefilming airblast breakup. Finally, SMD correlations from the literature are compared to the present experiment. Most of the correlations calibrated with LDA/LDT measurement underestimate the SMD. This highlights the need to use shadrowgraphy for calibrating primary breakup models.

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Section: Introductionmentioning

confidence: 99%

Influence of the ambient pressure on the liquid accumulation and on the primary spray in prefilming airblast atomization

Chaussonnet

Gepperth

Holz

et al. 2020

International Journal of Multiphase Flow

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show abstract

“…The lengthscale parameter h is often taken as a lengthscale based on a liquid phase scale (e.g. Bhayaraju and Hassa, 2009;Sauer et al, 2016). It seems reasonable to base the choice of the lengthscale h on the height of the liquid injection channel as done by Sauer et al (2016) and Ling et al (2017).…”

Section: Settings Of the Computationsmentioning

confidence: 99%

From High-Fidelity Numerical Simulations of a Liquid-Film Atomization to a Regime Classification

Bilger

Cant

2018

Atomiz Spr

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High-fidelity numerical simulations of spray formation were conducted with the aim of improving fundamental understanding of airblast liquid film atomisation. The gas/liquid interaction in the near nozzle region is investigated for a multitude of operating conditions in order to extrapolate phenomenological and breakup predictions. To reach this goal, the Robust Conservative Level Set (RCLS) method has been used. For a fixed prefilmer geometry, we performed a parametric study on the impact of various liquid and gas velocities on the topological evolution of the liquid interface. The behaviour and development of the liquid film is found to be influenced mainly by the relative inertia of the gas and the liquid, the liquid surface tension and interfacial shear stresses. Preliminary regime maps predicting the prefilming liquid-sheet atomisation behaviour are constructed based on our numerical results. Three distinct types of "regime" are reported: accumulation, ligament-merging and 3-D wave mode. In addition, these results also show the influence of vortex action and rim-driven dynamics on the breakup mechanism at the atomiser edge. An increase in liquid injection speed leads to the generation of smaller droplets whereas an increase in air velocity does not point to one simple conclusion.

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“…Of the two principal variants for prefilming, which are used throughout the industry, the pressure swirl atomizer-swirl cup and the prefilmer supplied from an annular channel between the swirlers, the latter possibility was chosen for a better definition of the initial condition of the film. Earlier research [1] had shown, that for the higher operating conditions of aeroengines, supercritical conditions exist for the film leading to atomization at the wave crests of the film and eventual dry out of the filmer ring. Hence a short prefilmer length is necessary to guarantee that all the fuel is atomized at the prefilmer lip.…”

Section: Burnermentioning

confidence: 99%

“…The purpose of the renewed constriction of the fuel path is the partial isolation of the coaxial fuel slot from the suction of the swirling air flow. Thereby the premature breakup of the film before the opening slot, which was observed in [1] for small film velocities, should be avoided. Apart from the small slot heights, which would not be allowed in a practical injector for reasons of airworthiness, no other means of thermal management were applied.…”

Section: Burnermentioning

confidence: 99%

Self-Exited Oscillation in a Combustion Chamber Driven by Phase Change in the Liquid Fuel Feed System

Hassa

Heinze²,

Meier³

et al. 2011

International Journal of Spray and Combustion Dynamics

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A new mechanism for the generation of a self-exited oscillation of combustion in a generic combustion chamber typical for aeroengine combustors is described. The cause of the oscillation is the phase change from liquid to vapour which happens when the preheat temperature of the air flowing through the burner exceeds the boiling temperature at the operating pressure and the fuel flow is so low that heat transfer to the liquid fuel causes evaporation within the fuel channels of the burner. Liquid fuel and vapour alternatively enter the airstream of the burner. This leads to an unstable situation for the flame. Measurements of chemiluminescence and liquid fuel show nearly complete extinction and re-ignition for the limit cycle. Prevention of the oscillation is possible by better thermal management of the fuel path.

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Planar Liquid Sheet Breakup of Prefilming and Nonprefilming Atomizers at Elevated Pressures

Cited by 32 publications

References 0 publications

Influence of the ambient pressure on the liquid accumulation and on the primary spray in prefilming airblast atomization

Influence of the ambient pressure on the liquid accumulation and on the primary spray in prefilming airblast atomization

From High-Fidelity Numerical Simulations of a Liquid-Film Atomization to a Regime Classification

Self-Exited Oscillation in a Combustion Chamber Driven by Phase Change in the Liquid Fuel Feed System

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