Steady three-dimensional patterns in gravity-driven film flow down an inclined sinusoidal bottom contour

Al-Shamaa, B.; Kahraman, T.; Wierschem, Andreas

doi:10.1063/5.0140841

Cited by 6 publications

(12 citation statements)

References 58 publications

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“…We note that the crossover from broken solitary waves to capillary turbulence at Reynolds numbers of approximately 23 coincides with the occurrence of a steady three-dimensional surface pattern further upstream; see figure 1(b). The average spanwise wavelength in the turbulent regime is slightly smaller than that of the steady pattern, where the wavelength was approximately 10 mm at Re = 30, and decreased to approximately 9 mm at higher Reynolds numbers (Al-Shamaa et al 2023).…”

Section: Resultsmentioning

confidence: 77%

“…Furthermore, the breaking of travelling solitary-wave fronts results in fingers that may interact also spanwise to the main flow direction. Hence resonant interaction of a triad formed by a pair of oblique modes with the wavy bottom contour is expected to be relevant, as in the steady three-dimensional pattern further upstream in the same system reported recently (Al-Shamaa, Kahraman & Wierschem 2023) or in travelling waves in film flows down flat inclines or in boundary layers (Kachanov 1994; Liu, Schneider & Gollub 1995).…”

Section: Introductionmentioning

confidence: 65%

“…Hence considering single steps up or down as done by Bontozoglou & Serifi (2008) is not sufficient, and inertia seems to be relevant. In view of the steady three-dimensional pattern upstream (Al-Shamaa et al 2023), resonance with the corrugations appears to promote wave breaking.…”

Section: Resultsmentioning

confidence: 99%

“…We employ shadowgraphy to obtain general spatiotemporal information about the free surface and light-sheet technique to acquire time series about the local surface elevation. The set-up of the shadowgraph technique is shown in figure 1(a) (Al-Shamaa et al 2023): the film surface was illuminated with the light of a 400 W halogen lamp reflected from the laboratory ceiling. It was imaged with a monochrome camera (1280 × 1024 pixels, 8 bit resolution, frame rate 15 fps).…”

Section: Experimental System and Set-upmentioning

confidence: 99%

“…We analysed time series of 8192 frames at crest numbers 43 and 58, corresponding to distances 425 mm and 575 mm from the channel inflow, at frame rate 172.53 fps. From the frames, the position of the free surface was determined at the peak of the crest with an edge detection code in MATLAB, as reported previously by Al-Shamaa et al (2023).…”

Section: Experimental System and Set-upmentioning

confidence: 99%

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Surface turbulence in film flow over periodic ripples

Al-Shamaa,

Wierschem

2024

J. Fluid Mech.

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Turbulence in gravity-driven film flow is usually discussed in terms of three-dimensional solitary-wave pulses as they are frequently observed in flows along smooth walls. Here, we show that free-surface turbulence arises in films along rippled substrates, as they are commonly employed in process engineering applications, already at rather low Reynolds numbers from the irregular break-up of the solitary-wave fronts. Short waves in the capillary regime replace the broken solitary waves beyond a certain Reynolds number. The crossover coincides with the occurrence of steady three-dimensional surface patterns upstream, which suppress travelling waves. The waves show power spectral densities with power-law exponents typical for weak capillary-wave turbulence. With increasing Reynolds number, the steepness of the power law declines to lower levels.

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Section: Resultsmentioning

confidence: 77%

Section: Introductionmentioning

confidence: 65%

Section: Resultsmentioning

confidence: 99%

Section: Experimental System and Set-upmentioning

confidence: 99%

Section: Experimental System and Set-upmentioning

confidence: 99%

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Surface turbulence in film flow over periodic ripples

Al-Shamaa,

Wierschem

2024

J. Fluid Mech.

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Flow of viscoelastic films over grooved surfaces with partial wetting

Pettas,

Karapetsas,

Syrakos

et al. 2024

J. Fluid Mech.

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We consider the steady flow of a viscoelastic film over an inclined plane featuring periodic trenches normal to the main flow direction. The trenches have a square cross-section and side length 5–8 times the capillary length. Owing to the orientation of the substrate, the film fails to coat the topographical feature entirely, forming a second gas–liquid interface inside the trench and two three-phase contact lines at the points where the free surface meets the wall of the trench. The volume of entrapped air depends on material and flow parameters and geometric conditions. We develop a computational model and carry out detailed numerical simulations based on the finite element method to investigate this flow. We solve the two-dimensional mass and momentum conservation equations using the exponential Phan-Thien & Tanner constitutive model to account for the rheology of the viscoelastic material. Due to the strong nonlinearity, multiple steady solutions possibly connected by turning points forming hysteresis loops, transcritical bifurcations and isolated solution branches are revealed by pseudo-arc-length continuation. We perform a thorough parametric analysis to investigate the combined effects of elasticity, inertia, capillarity and viscosity on the characteristics of each steady flow configuration. The results of our simulations indicate that fluid inertia and elasticity may or may not promote wetting, while shear thinning and hydrophilicity always promote the wetting of the substrate. Interestingly, there are conditions under which the transition to the inertial regime is not smooth, but a hysteresis loop arises, signifying an abrupt change in the film hydrodynamics. Additionally, we investigate the effect of the geometrical characteristics of the substrate, and our results indicate that there is a unique combination of the geometry and viscoelastic properties that either maximizes or minimizes the wetting lengths.

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Evolution of turbulent liquid films on the corrugated plate—rivulets and slender water columns necking rupture

Zeng,

Wang,

et al. 2023

Physics of Fluids

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The evolution of turbulent liquid film on the corrugated plate is experimentally studied with the help of ultrasonic Doppler velocimetry and a high-speed camera, revealing the formation mechanism of rivulets and water columns necking rupture. The results show that the flow pattern of the liquid film on the corrugated plate is divided into three regions: stable region, fluctuating region, and oscillating region. In the fluctuating region, the connection between adjacent solitary waves leads to the generation of primary rivulets. In contrast, the formation of secondary rivulets mainly comes from the extinction of solitary waves. In the oscillating region, the collision between secondary rivulets promotes the formation of slender water columns. The necking diameter of the water column tended to decrease exponentially with time. The increase in Rel (liquid phase Reynolds number) promotes the necking rupture process of the water column due to the presence of corrugated structures. When Rel increased from 1.72 × 104 to 2.57 × 104, the characteristic time of necking rupture was shortened by about 25.7%.

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Steady three-dimensional patterns in gravity-driven film flow down an inclined sinusoidal bottom contour

Cited by 6 publications

References 58 publications

Surface turbulence in film flow over periodic ripples

Surface turbulence in film flow over periodic ripples

Flow of viscoelastic films over grooved surfaces with partial wetting

Evolution of turbulent liquid films on the corrugated plate—rivulets and slender water columns necking rupture

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