Stability of gravity-driven thin-film flow in the presence of an adjacent gas phase

Kushnir, R.; Barmak, Ilya; Ullmann, Amos; Brauner, Neima

doi:10.1016/j.ijmultiphaseflow.2020.103443

Cited by 5 publications

(9 citation statements)

References 51 publications

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“…On the other hand, recent investigations suggest that strong confinements may, in fact, lower the risk of flooding. Lavalle et al (2019) have shown that the Kapitza instability can be entirely suppressed by sufficiently confining the gas, as suggested by Tilley, Davis & Bankoff (1994) and confirmed by Kushnir et al (2021), and that this is facilitated by low tilt angles. Further, the authors observed that the linear stabilization, which they confirmed experimentally, is amplified by increasing the counter-current gas flow rate.…”

Section: Introductionmentioning

confidence: 75%

“…At the largest η (filled squares, η = 3.9), the growth rate increases monotonically with |Re g |, implying a gas-induced destabilization, up to the onset of absolute instability (AI), where −k imax diverges (Vellingiri et al 2015). Conversely, at very small η values (open squares and pentagons, η = 2, 2.8), the effect of the gas is monotonically stabilizing, up to the point of fully suppressing (S) the long-wave Kapitza instability (Lavalle et al 2019;Kushnir et al 2021). In the intermediate range (crosses, Figure 2(c) plots the upper and lower relative film height deflections h max /h − 1 and h min /h − 1 for nonlinear TWS at ω = ω max , whereh = Λ −1 Λ 0 h dx is the film height averaged over one wavelength, withh / = h 0 in the case of nonlinear waves.…”

Section: Resultsmentioning

confidence: 99%

“…2019; Kushnir et al. 2021). In the intermediate range (crosses, asterisks and diamonds, , 3.1 and 3.4), the behaviour is non-monotonic, stabilization occurring at low and destabilization at large values of .…”

Section: Resultsmentioning

confidence: 99%

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Superconfined falling liquid films: linear versus nonlinear dynamics

et al. 2021

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Section: Introductionmentioning

confidence: 75%

Section: Resultsmentioning

confidence: 99%

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Superconfined falling liquid films: linear versus nonlinear dynamics

et al. 2021

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“…Moreover, they discovered that the gas-induced stabilization is strongest in the counter-current configuration, and increases with increasing magnitude of the gas flow rate. Kushnir et al (2021) showed subsequently that stabilization also occurs in the case of a confined recirculating gas, i.e. when the net gas flow rate is zero.…”

Section: Introductionmentioning

confidence: 99%

Gas-sheared falling liquid films beyond the absolute instability limit

Ishimura,

Mergui,

Ruyer-Quil

et al. 2023

J. Fluid Mech.

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We study the effect of a confined turbulent counter-current gas flow on the waviness of a weakly inclined falling liquid film. Our study is centred on experiments in a channel of 13 mm height, using water and air, where we have successively increased the counter-current gas flow rate until flooding. Computations with a new low-dimensional model and linear stability calculations are used to elucidate the linear and nonlinear wave dynamics. We find that the gas pressure gradient plays an important role in countering the stabilizing effect of the tangential gas shear stress at the liquid–gas interface. At very low inclination angles, the latter effect dominates and can suppress the long-wave Kapitza instability unconditionally. By contrast, for non-negligible inclination, the gas effect is linearly destabilizing, amplifies the height of nonlinear Kapitza waves, and exacerbates coalescence-induced formation of large-amplitude tsunami waves. Kapitza waves do not undergo any catastrophic transformation when the counter-current gas flow rate is increased beyond the absolute instability (AI) limit. On the contrary, we find that AI is an effective linear wave selection mechanism in a noise-driven wave evolution scenario, leading to highly regular downward-travelling nonlinear wave trains, which preclude coalescence events. In our experiments, where Kapitza waves develop in a protected region before coming into contact with the gas, flooding is eventually caused far beyond the AI limit by upward-travelling short-wave ripples. Based on our linear stability calculations for arbitrary wavenumbers, we have uncovered a new short-wave interfacial instability mode with negative linear wave speed, causing these ripples.

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“…The strong stabilizing effect induced by a counter-current air flow on a wavy water film is reproduced by Trifonov (2019) at small inclination and strong confinement. Kushnir et al (2021), via a comprehensive parametric study, have recently established that regimes of linear stabilization in the case of a zero net gas flow occur for channel heights H 10 mm at β = 1 • and H 2 mm at β = 10 • in water/air system. Furthermore, when the gas flows counter-currently, it was shown in Lavalle et al (2019) that the linear stabilization is intensified over the entire range of unstable wave numbers when the confinement is sufficiently strong.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear wave attenuation in strongly confined falling liquid films sheared by a laminar counter-current gas flow

Mergui

Lavalle

et al. 2023

J. Fluid Mech.

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Experiments are conducted in water films falling along the bottom wall of a weakly inclined rectangular channel of height $5$ mm in the presence of a laminar counter-current air flow. Boundary conditions have been specifically designed to avoid flooding at the liquid outlet, thus allowing us to focus on the wave dynamics in the core of the channel. Surface waves are excited via coherent inlet forcing before they come into contact with the air flow. The effect of the air flow on the height, shape and speed of two-dimensional travelling nonlinear waves is investigated and contrasted with experiments of Kofman, Mergui & Ruyer-Quil (Intl J. Multiphase Flow, vol. 95, 2017, pp. 22–34), which were performed in a weakly confined channel. We observe a striking difference between these two cases. In our strongly confined configuration, a monotonic stabilizing effect or a non-monotonic trend (i.e. the wave height first increases and then diminishes upon increasing the gas flow rate) is observed, in contrast to the weakly confined configuration where the gas flow is always destabilizing. This stabilizing effect implies the possibility of attenuating waves via the gas flow and it confirms recent numerical results obtained by Lavalle et al. (J. Fluid Mech., vol. 919, 2021, R2) in a superconfined channel.

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Stability of gravity-driven thin-film flow in the presence of an adjacent gas phase

Cited by 5 publications

References 51 publications

Superconfined falling liquid films: linear versus nonlinear dynamics

Superconfined falling liquid films: linear versus nonlinear dynamics

Gas-sheared falling liquid films beyond the absolute instability limit

Nonlinear wave attenuation in strongly confined falling liquid films sheared by a laminar counter-current gas flow

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