Spanwise structuring and rivulet formation in suspended falling liquid films

Manuel Rietz, Reinhold Kneer, Benoit Scheid, and Wilko Rohlfs
Phys. Rev. Fluids 6, 084805 – Published 25 August 2021

Abstract

In suspended falling films, i.e., films on the underside of a bounding wall with arbitrary inclination, the surface film topology evolves towards a distinct spanwise structuring of the flow into rivulets, which is potentially accompanied by dripping events. Experimental data suggest a connection between long-term spanwise structuring and primary instabilities of the film surface. However, available experimental data regarding this connection remain nonconclusive. Hence, the present study aims at elucidating the evolution of a suspended falling film from varying imposed initial conditions to the emergence of spanwise modulations and rivulet formation. The study is carried out by means of extended numerical simulations employing a weighted residual integral boundary layer model for falling liquid films. The investigated parameter space covers recent experimental data on the topic. Varying imposed initial conditions, Reynolds number, Kapitza number, as well as wall inclination, several possible causes for a deviation of observed spanwise wavelengths from the one predicted by the primary Rayleigh-Taylor mechanism, are identified. This includes a distinct influence of initial conditions, asynchronous destabilization of consecutive wavefronts, competing short wave capillary instabilities, and rivulet interaction.

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  • Received 23 November 2020
  • Accepted 15 July 2021

DOI:https://doi.org/10.1103/PhysRevFluids.6.084805

©2021 American Physical Society

Physics Subject Headings (PhySH)

Fluid Dynamics

Authors & Affiliations

Manuel Rietz* and Reinhold Kneer3

  • Institute of Heat and Mass Transfer, RWTH Aachen University, Augustinerbach 6, 52056 Aachen, Germany

Benoit Scheid

  • TIPs, Université libre de Bruxelles, Avenue Franklin D. Roosevelt 50, 1050 Brussels, Belgium

Wilko Rohlfs

  • Department of Thermal and Fluid Engineering, University of Twente, Drienerlolaan 5, 7522 NB Enschede, The Netherlands

  • *rietz@wsa.rwth-aachen.de

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Vol. 6, Iss. 8 — August 2021

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