Non-modal stability analysis of stratified two-phase channel flows

Barmak, Ilya; Gelfgat, Alexander; Ullmann, Amos; Brauner, Neima

doi:10.1016/j.ijmultiphaseflow.2018.10.020

Cited by 13 publications

(5 citation statements)

References 31 publications

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“…Similar secondary peaks are also observed for other holdups, where the instability is predicted to be short wave. We assume that these peaks correspond to the eigenmodes with relatively small decay rates, which can also be excited by the noise, or by non-modal instability (Barmak, (2019)). We address these frequencies below, when discussing the holdup range corresponding to the long wave instability.…”

Section: Resultsmentioning

confidence: 99%

Experimental and numerical study of primary instability of a two-phase stratified flow in a circular pipe

Nezihovski,

Barmak,

Gelfgat

et al. 2024

Preprint

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The onset of the primary instability of two-phase air-water stratified flow in a circular pipe was studied experimentally by two independent non-intrusive techniques. The techniques analyze the steady or oscillatory response of either a laser beam passing through the air-water interface, or of an echo of an ultrasound wave reflected from the interface. The experiments are accompanied by linear stability analysis performed in both Cartesian and bipolar coordinates, thus yielding two independently obtained numerical results for comparison. The critical values of the phases’ superficial velocities corresponding to the flow primary instability calculated numerically by the two independent methods agree well with each other. The computed stability diagram shows that instability sets in owing to long-wave disturbances at large holdups, while at smaller holdups, the most unstable perturbations appear as finite-length (short) waves. A comparison of the experimental and numerical results shows a good agreement for the long-wave instability. For the short-wave instability, the measured critical superficial velocities are below the computed ones, while the frequencies found experimentally for supercritical oscillatory flow states agree with the numerical predictions. Several additional peaks in the frequency spectra are observed in the experiments. By comparing these frequencies with the numerical spectra, we argue that they correspond to stable eigenmodes with close to zero decay rates, which can be triggered either by non-linear mechanisms, or become unstable because of experimental imperfections.

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Section: Resultsmentioning

confidence: 99%

Experimental and numerical study of primary instability of a two-phase stratified flow in a circular pipe

Nezihovski,

Barmak,

Gelfgat

et al. 2024

Preprint

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show abstract

“…The above equations must be solved together with no-slip boundary conditions at the duct walls, continuity of velocity and viscous stresses at the interface, and the kinematic condition for the interface perturbation. The whole set of the linearized boundary conditions (see also Barmak et al, 2019) are listed below. The no-slip conditions:…”

Section: Linearized Stability Problemmentioning

confidence: 99%

Instability of stratified two-phase flows in rectangular ducts

Gelfgat

Brauner

2020

International Journal of Multiphase Flow

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“…Owing to the inherent modelling complexity of the flow, literature in the field of oil-water transportation inside pipes and channels is almost entirely based on experimental investigations, focused mainly on the evaluation of flow regimes/global flow properties such as pressure drop and flow rate (Sotgia, Tartarini & Stalio 2008), and on single-point measurements of the interface deformation (Issenmann, Laroche & Falcon 2016), but also on analytical investigations of flow stability (Barmak et al 2016(Barmak et al , 2019.…”

Section: Introductionmentioning

confidence: 99%

Propagation of capillary waves in two-layer oil–water turbulent flow

et al. 2023

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We study the dynamics of capillary waves at the interface of a two-layer stratified turbulent channel flow. We use a combined pseudo-spectral/phase field method to solve for the turbulent flow in the two liquid layers and to track the dynamics of the liquid–liquid interface. The two liquid layers have same thickness and same density, but different viscosity. We vary the viscosity of the upper layer (two different values) to mimic a stratified oil–water flow. This allows us to study the interplay between inertial, viscous and surface tension forces in the absence of gravity. In the present set-up, waves are naturally forced by turbulence over a broad range of scales, from the larger scales, whose size is of order of the system scale, down to the smaller dissipative scales. After an initial transient, we observe the emergence of a stationary capillary wave regime, which we study by means of temporal and spatial spectra. The computed frequency and wavenumber power spectra of wave elevation are in line with previous experimental findings and can be explained in the frame of the weak wave turbulence theory. Finally, we show that the dispersion relation, which gives the frequency ( $\omega$ ) as a function of the wavenumber ( $k$ ), is in good agreement with the well-established theoretical prediction, $\omega (k) \sim k^{3/2}$ .

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Non-modal stability analysis of stratified two-phase channel flows

Cited by 13 publications

References 31 publications

Experimental and numerical study of primary instability of a two-phase stratified flow in a circular pipe

Experimental and numerical study of primary instability of a two-phase stratified flow in a circular pipe

Instability of stratified two-phase flows in rectangular ducts

Propagation of capillary waves in two-layer oil–water turbulent flow

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