Measurements of liquid film flow as a function of fluid properties and channel width: Evidence for surface-tension-induced long-range transverse coherence

Georgantaki, A; Vatteville, Judith; Vlachogiannis, M.; Bontozoglou, V.

doi:10.1103/physreve.84.026325

Cited by 27 publications

(32 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the present experiments, its value is kept constant at Ka = 110. This value is low enough to make the recently discovered (Georgantaki et al 2011) effect of sidewalls on the primary instability practically insignificant.…”

Section: Experimental Methodologymentioning

confidence: 91%

Experimental evidence for a short-wave global mode in film flow along periodic corrugations

2013

Self Cite

View full text Add to dashboard Cite

The primary instability of liquid film flow along periodically corrugated substrates is studied experimentally. Two different wall shapes, of the same wavelength and height, are tested for a wide range of inclinations. It is found that, beyond a specific inclination, a new instability mode occurs before the classical, convective, long-wave one. This is a short, travelling wave, which is highly regular and persistently twodimensional, and appears to be a global mode. The exact shape of the corrugations has a leading-order effect on the inclination at which the new mode appears and on its wavelength at inception. Compared with the behaviour of film flow on a flat substrate, the presently tested periodic walls are found to delay very significantly, but each one to a different extent, the onset of the primary instability. This delay increases with inclination, and presents a distinct discontinuity when transition from the long-to the short-wave mode takes place.

show abstract

Section: Experimental Methodologymentioning

confidence: 91%

Experimental evidence for a short-wave global mode in film flow along periodic corrugations

2013

Self Cite

View full text Add to dashboard Cite

show abstract

“…Meanwhile, spanwise flow in the visco-capillary region for cases 1 to 3 is entirely dominated by curvature-induced pressure variations due to the absence of gravity in this direction (the latter point has recently been made by Georgantaki et al (2011)). This is illustrated representatively for case 1 (at a given streamwise z-y slice in the visco-capillary region) in figure 21, showing the occurrence of a cellular flow pattern within the spanwise succession of capillary humps and troughs.…”

Section: The Visco-capillary Regionmentioning

confidence: 93%

“…As shown in figure 15(c), the driving force for the spanwise flow within the leading hump results from a spanwise wall pressure gradient, ∂ z p w , caused by a change in free-surface curvature between the large hump and the trough of the first capillary wave (through the effect of capillary forces). This mechanism is particularly effective in the spanwise direction, as it is not counteracted by gravity, and has recently been invoked by Georgantaki et al (2011) to explain the stabilization of curved wave fronts spanning the width of laterally confined inclined film flows. It forces near-wall liquid from the hump to the capillary trough, thus driving the vortex.…”

Section: The Inertia-dominated Regionmentioning

confidence: 96%

“…Conversely, when the falling film is significantly confined by sidewalls, as may be the case in experimental realizations, the lateral boundary conditions already impose a three-dimensional primary flow. Depending on the sidewall separation distance, this can cause any (quasi-)two-dimensional wave dynamics to be practically bypassed (Vlachogiannis et al 2010;Georgantaki et al 2011;Pollak, Haas & Aksel 2011).…”

Section: Introductionmentioning

confidence: 98%

See 1 more Smart Citation

Three-dimensional flow structures in laminar falling liquid films

et al. 2014

View full text Add to dashboard Cite

Full numerical simulations of the Navier-Stokes equations for four cases of vertically falling liquid films with three-dimensional surface waves have been performed. Flow conditions are based on several previous experimental studies where the streamwise and spanwise wavelengths were imposed, which we exploit by simulating periodic wave segments. The considered flows are laminar but approach conditions at which intermittent wave-induced turbulence has been observed elsewhere. Working liquids range from water to silicone oil and cover a large interval of the Kapitza number (Ka = 18-3923), which relates capillary to viscous forces. Simulations were performed on a supercomputer, using a finite-volume code and the volume of fluid and continuum surface force methods to account for the multiphase nature of the flow. Our results show that surface waves, consisting of large horseshoe-shaped wave humps concentrating most of the liquid and preceded by capillary ripples on a thin residual film, segregate the flow field into two regions: an inertia-dominated one in the large humps, where the local Reynolds number is up to five times larger than its mean value, and a visco-capillary region, where capillary and/or viscous forces dominate. In the inertial region, an intricate structure of different-scale vortices arises, which is more complicated than film thickness variations there suggest. Conversely, the flow in the visco-capillary region of large-Ka fluids is entirely governed by the local free-surface curvature through the action of capillary forces, which impose the pressure distribution in the liquid film. This results in flow separation zones underneath the capillary troughs and a spanwise cellular flow pattern in the region of capillary wave interference. In some cases, capillary waves bridge the large horseshoe humps in the spanwise direction, coupling the two aforementioned regions and leading the flow to oscillate between three-and two-dimensional wave patterns. This persists over long times, as we show by simulations with the low-dimensional model of Scheid et al. (J. Fluid Mech., vol. 562, 2006, pp. 183-222) after satisfactory comparison with our direct simulations at short times. The governing mechanism is connected to the bridging capillary waves, which drain liquid from the horseshoe humps, decreasing their amplitude and wave speed and causing them to retract in the streamwise direction. Overall, it is observed that spanwise flow structures (not accounted for in two-dimensional investigations) are particularly complex due to the absence of gravity in this direction.

show abstract

“…It is notable that an unequivocal experimental confirmation of the linear prediction was also delayed significantly (Liu, Paul & Gollub 1993), and that an unexpected strong effect of the channel width was reported very recently by Georgantaki et al (2011) and Pollak, Haas & Aksel (2011).…”

mentioning

confidence: 90%

The role of surfactants on the mechanism of the long-wave instability in liquid film flows

Karapetsas

Bontozoglou

2014

J. Fluid Mech.

View full text Add to dashboard Cite

The analysis for the physical mechanism of the long-wave instability in liquid film flow is extended to take into account the presence of a surfactant of arbitrary solubility. The Navier–Stokes equations are supplemented by mass balances for the concentrations at the interface and in the bulk, by a Langmuir model for adsorption kinetics at the interface, and are expanded in the limit of long-wave disturbances. The longitudinal flow perturbation, known to result from the perturbation shear stress which develops along the deformed interface, is shown to contribute a convective flux that triggers an interfacial concentration gradient. This gradient is, at leading order, in phase with the interfacial deformation, and as a result produces Marangoni stresses that stabilize the flow. The strength of the interfacial concentration gradient is shown to be maximum for an insoluble surfactant and to decrease with increasing surfactant solubility. The decrease is explained in terms of the spatial phase of mass transfer between interface and bulk, which mitigates the interfacial flux by the flow perturbation and leads to the attenuation of Marangoni stresses. Higher-order terms are derived, which provide corrections for disturbances of finite wavelength

show abstract

Measurements of liquid film flow as a function of fluid properties and channel width: Evidence for surface-tension-induced long-range transverse coherence

Cited by 27 publications

References 20 publications

Experimental evidence for a short-wave global mode in film flow along periodic corrugations

Experimental evidence for a short-wave global mode in film flow along periodic corrugations

Three-dimensional flow structures in laminar falling liquid films

The role of surfactants on the mechanism of the long-wave instability in liquid film flows

Contact Info

Product

Resources

About