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Three-dimensional wave regimes on vertically falling liquid films: Downstream evolution of statistical characteristics.

Name
Alexandr
Surname
Kvon
Scientific organization
Novosibirsk State University
Academic degree
Ph.D. candidate
Position
laboratory assistant
Scientific discipline
Mathematics & Mechanics
Topic
Three-dimensional wave regimes on vertically falling liquid films: Downstream evolution of statistical characteristics.
Abstract
The experimental study of 3D wave characteristics as well as study of transition process from 2D

to 3D waves for liquid films falling down a vertical plate was conducted. The LIF method was

used to obtain instant shapes of waves. During 2D-3D wave transition, a strong transverse

redistribution of liquid leading to the formation of rivulets on the surface of liquid film takes

place. Obtained data were used to calculate various statistical characteristics such as dispersion,

PDF and PSD.
Keywords
laser induced fluorescence, 3D wavy liquid film, PDF, PSD,
Summary

Three-dimensional (3D) wave regimes are considered to be the last stage of the film flow

evolution at moderate Reynolds numbers. In such regimes surface of the film is covered with

numerous 3D waves. Therefore statistical approaches are often involved in order to describe

these wave regimes.

Results of experimental study of 3D wave characteristics as well as study of transition process

from two-dimensional (2D) to 3D waves for liquid films falling down a vertical plate are

presented. Experiments were carried out in the range of Reynolds numbers 5 < Re < 100. Liquids

with various physical properties were used as working fluids. The whole flow structure was

registered using shadowgraph method. It was found that rivulets formation takes place during the

process of transition from 2D to 3D wave motion. Size of the forming rivulets is weakly affected

by Re, however rivulets’ evolution depends on flow parameters. Detailed structures of the waves

were studied by means of the high speed laser induced fluorescence (LIF) method, which makes

it possible to obtain instantaneous forms of 3D waves. Obtained film thickness data were used to

calculate various statistical characteristics such as dispersion values, probability density

functions (PDF), spectral power densities of film thickness fluctuations, mean film thickness

distribution etc. Extensive statistical analysis showed that rivulets’ behavior is depending on

prior characteristics of 2D waves in the upper part of film flow. Immovable or randomly shifting

in transverse direction rivulets can be observed. On time-averaged (t=0.7s) cross sections

different amount of rivulets can be observed for different moments in time. The statistical

analysis also allows us to suggest that stabilization of 3D wave motion occurs at relatively short

distances from liquid inflow for the flow regimes with high Reynolds numbers whereas at lower

Re continuous downstream evolution of the wave characteristics with gradual damping of the

waves is observed.