Acoustically excited air-assisted liquid sheets

Sivadas, V.; Fernandes, Edgar C.; Heitor, M. V.

doi:10.1007/s00348-003-0618-9

Cited by 18 publications

(5 citation statements)

References 13 publications

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“…Also, at a fixed frequency, the amplitude of sheet undulation/flapping increased with the sound intensity. Sivadas et al 11 introduced acoustic disturbances in the coaxial flow of air over the top and bottom surfaces of a planar liquid sheet. The breakup length was seen to be a good measure of the stability of the liquid sheet.…”

Section: Introductionmentioning

confidence: 99%

Instability of a moving liquid sheet in the presence of acoustic forcing

2010

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The excitation of thin planar liquid sheets formed by impinging two collinear water jets to acoustic waves was studied at varying frequencies and sound pressure levels ͑SPLs͒. Experiments were conducted over a range of liquid velocities that encompassed the stable and flapping regimes of the sheet. For a given frequency, there was a threshold value of SPL below which the sheet was unaffected. The threshold SPL increased with frequency. Further, the sheet was observed to respond to a set of specific frequencies lying in the range of 100-300 Hz, the frequency set varying with the Weber number of the liquid sheet. The magnitude of the response for a fixed pressure level, characterized by the reduction in the extent of the sheet, was larger at lower frequencies. The droplet sizes formed by the disintegration of the sheet reduced with an increase in the measured response and the drop-shedding frequency was near the imposed frequency. Model equations for inviscid flow and accounting for the varying pressure field across the moving liquid sheet of constant thickness was solved to determine the linear stability of the system. Numerical solution shows that the most unstable wavelengths in the presence of the forcing to be smaller than in the absence, which is in line with observations. Both the dilatational and sinuous modes are coupled at the lowest order and become significant for the range of acoustic forcing studied. The model calculation suggests that the parametric resonance involving the dilatational mode may be responsible for the observed instability although the model was unable to predict the observed variation of threshold SPL with frequency.

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Section: Introductionmentioning

confidence: 99%

Instability of a moving liquid sheet in the presence of acoustic forcing

2010

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“…The resonant characteristics of the present atomizer configuration were established by correlating the pressure wave behavior at the loudspeaker and at the outlet of the injector. 5 In other words, measurements with a microphone at the sound source and outlet show that the minimum phase-difference and peak energy transfer occurs at the optimum frequency of 750Hz.…”

Section: Resultsmentioning

confidence: 99%

Visualization Studies of an Acoustically Excited Liquid Sheet

Sivadas

Heitor

2002

Annals of the New York Academy of Sciences

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The interaction between atomizing air and a liquid sheet initiates interfacial instabilities that develop into large amplitude waves, which ultimately promote liquid disintegration. However, to reduce atomizing airflow, the dynamic influence of the surrounding gas is not sufficient to affect the inner core of the liquid. In other words, the characteristic length scales of perturbation promoting break-up are small in comparison with the initial liquid momentum. Therefore, to enhance the disintegration process, the intact liquid-core near the nozzle outlet must be influenced by artificial or external excitations. To accomplish this, the present investigation employed a plane laminar liquid-sheet that was perturbed by acoustic excitations at an optimum frequency through the impinging air-streams.

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“…In the acoustic field parallel to the jet stream, Sivadas, Fernandes & Heitor (2003) and Sivadas et al (2016) experimentally investigated the breakup length of the liquid jet and the sheet corresponding to the sound intensity; they established empirical formulas between the breakup length and the acoustic number. More recently, Chaussonnet et al (2017) conducted an experimental study on prefilming airblast atomization in an oscillating air flow field and obtained a SMD prediction model based on linear stability theory in a steady basic flow.…”

Section: Introductionmentioning

confidence: 99%

“…In the acoustic field parallel to the jet stream, Sivadas, Fernandes & Heitor (2003) and Sivadas et al. (2016) experimentally investigated the breakup length of the liquid jet and the sheet corresponding to the sound intensity; they established empirical formulas between the breakup length and the acoustic number.…”

Section: Introductionmentioning

confidence: 99%

Experimental study on the oscillatory Kelvin–Helmholtz instability of a planar liquid sheet in the presence of axial oscillating gas flow

et al. 2023

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The oscillatory Kelvin–Helmholtz (K–H) instability of a planar liquid sheet was experimentally investigated in the presence of an axial oscillating gas flow. An experimental system was initiated to study the oscillatory K–H instability. The surface wave growth rates were measured and compared with theoretical results obtained using the authors’ early linear method. Furthermore, in a larger parameter range experimentally studied, it is interesting that there are four different unstable modes: first disordered mode (FDM), second disordered mode (SDM), K–H harmonic unstable mode (KHH) and K–H subharmonic unstable mode (KHS). These unstable modes are determined by the oscillating amplitude, oscillating frequency and liquid inertia force. The frequencies of KHH are equal to the oscillating frequency; the frequency of KHS equals half the oscillating frequency, while the frequencies of FDM and SDM are irregular. By considering the mechanism of instability, the instability regime maps on the relative Weber number versus liquid Weber number (Werel–Wel) and the Weber number ratio versus the oscillating frequency (Werel/Wel– $\varOmega$ s2) were plotted. Among these four modes, KHS is the most unexpected: the frequency of this mode is not equal to the oscillating frequency, but the surface wave can also couple with the oscillating gas flow. Linear instability theory was applied to divide the parameter range between the different unstable modes. According to linear instability theory, K–H and parametric unstable regions both exist. However, note that all four modes (KHH, KHS, FDM and SDM) corresponded primarily to the K–H unstable region obtained from the theoretical analysis. Nevertheless, the parametric unstable mode was also observed when the oscillating frequency and amplitude were relatively low, and the liquid inertia force was relatively high. The surface wave amplitude was small but regular, and the evolution of this wave was similar to that of Faraday waves. The wave oscillating frequency was half that of the surface wave.

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Acoustically excited air-assisted liquid sheets

Cited by 18 publications

References 13 publications

Instability of a moving liquid sheet in the presence of acoustic forcing

Instability of a moving liquid sheet in the presence of acoustic forcing

Visualization Studies of an Acoustically Excited Liquid Sheet

Experimental study on the oscillatory Kelvin–Helmholtz instability of a planar liquid sheet in the presence of axial oscillating gas flow

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