DNS of falling film structure and heat transfer via MARS method

Kunugi, Tomoaki; Kino, Chiaki

doi:10.1016/j.compstruc.2004.08.018

Cited by 48 publications

(22 citation statements)

References 8 publications

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“…17 As discussed by Gao et al, 4 in other direct numerical calculations [19][20][21] periodic boundary conditions were used which enforce conservation of mean film thickness and limit the study to single developed waves. In recent direct numerical simulations, 5,22 the study is limited to low Reynolds numbers due to back-flow from the exit, caused by the imposition of other outflow boundary conditions.…”

Section: Governing Equations Boundary and Initial Conditionsmentioning

confidence: 99%

Flow structure underneath the large amplitude waves of a vertically falling film

Malamataris

Balakotaiah

2008

AIChE Journal

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in Wiley InterScience (www.interscience.wiley.com).Numerical solutions of the two-dimensional Navier-Stokes equations for vertically falling films show that when the wave amplitude exceeds a certain magnitude, two hyperbolic points on the wall and an elliptic point in the film are generated below the minimum of the wave and travel at the wave velocity. The shear stress along the wall between the hyperbolic points becomes negative and the instantaneous flow field in the film shows roll formation with flow reversal near the wall region. As the wave amplitude increases further, these rolls expand to the free surface dividing the film into regions of up and down flows. For high Kapitza number fluids such as water, multiple regions of up-flow and negative wall shear stress exist with their width oscillating in time. The flow field is interpreted in both stationary and moving frames of reference and in explaining transport enhancements at the wall and free surface.

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Section: Governing Equations Boundary and Initial Conditionsmentioning

confidence: 99%

Flow structure underneath the large amplitude waves of a vertically falling film

Malamataris

Balakotaiah

2008

AIChE Journal

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“…Secondly, although it is known that three-dimensional surface waves intensify heat and mass transfer between film and wall as well as across the free surface (Alekseenko et al 1994;Kunugi & Kino 2005;Demekhin et al 2007a), underlying intensification mechanisms have not been fully elucidated. Our DNS evince a number of three-dimensional flow structures causing the intensification of convective transport within the film.…”

Section: Introductionmentioning

confidence: 98%

“…Liu et al (1992Liu et al ( , 1995 proved the two scenarios experimentally and showed that high-frequency single-peaked waves develop checkerboard and waves with large separations develop synchronous spanwise patterns. A numerical confirmation of the synchronous evolution scenario was provided by the spatio-temporal direct numerical simulations (DNS) of Kunugi & Kino (2005). A clear picture of the wave topology resulting from synchronous instability was provided by the experiments of Park & Nosoko (2003).…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional flow structures in laminar falling liquid films

et al. 2014

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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.

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“…This phenomenon was first noted by Portalski (1964) and Massot, Irani & Lightfoot (1966), and was later investigated in more detail in terms of the underlying mechanisms (Dietze, Leefken & Kneer 2008;Dietze, Al-Sibai & Kneer 2009) and the influence of inertia, wave frequency and inclination angle (Malamataris & Balakotaiah 2008;Chakraborty et al 2014;Rohlfs & Scheid 2015). Numerical simulations conducted by Kunugi & Kino (2005) demonstrated a considerable enhancement of the heat and mass transport characteristics of the film as a result of flow reversal.…”

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confidence: 96%

Solitary waves on falling liquid films in the inertia-dominated regime

et al. 2018

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We offer new insights and results on the hydrodynamics of solitary waves on inertiadominated falling liquid films using a combination of experimental measurements, direct numerical simulations (DNS) and low-dimensional (LD) modelling. The DNS are shown to be in very good agreement with experimental measurements in terms of the main wave characteristics and velocity profiles over the entire range of investigated Reynolds numbers. And, surprisingly, the LD model is found to predict accurately the film height even for inertia-dominated films with high Reynolds numbers. Based on a detailed analysis of the flow field within the liquid film, the hydrodynamic mechanism responsible for a constant, or even reducing, maximum film height when the Reynolds number increases above a critical value is identified, and reasons why no flow reversal is observed underneath the wave trough above a critical Reynolds number are proposed. The saturation of the maximum film height is shown to be linked to a reduced effective inertia acting on the solitary waves as a result of flow recirculation in the main wave hump and in the moving frame of reference. Nevertheless, the velocity profile at the crest of the solitary waves remains parabolic and self-similar even after the onset of flow recirculation. The upper limit of the Reynolds number with respect to flow reversal is primarily the result of steeper solitary waves at high Reynolds numbers, which leads to larger streamwise pressure gradients that counter flow reversal. Our results should be of interest in the optimisation of the heat and mass transport characteristics of falling liquid films and can also serve as a benchmark for future model development.

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DNS of falling film structure and heat transfer via MARS method

Cited by 48 publications

References 8 publications

Flow structure underneath the large amplitude waves of a vertically falling film

Flow structure underneath the large amplitude waves of a vertically falling film

Three-dimensional flow structures in laminar falling liquid films

Solitary waves on falling liquid films in the inertia-dominated regime

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