Emergence of Kelvin-Helmholtz instabilities in shallow mixing layers: An experimental study

S. Proust, C. Berni, V. I. Nikora

Research output: Chapter in Book/Report/Conference proceedingPublished conference contribution


Free-surface shallow mixing layers behind a splitter plate were studied in a flume of rectangular cross-section consisting of a bed and sidewalls made of glass. The focus is on the effects on the emergence of horizontal Kelvin-Helmholtz-type coherent structures (KHCSs) of vertical flow confinement (i.e., flow depth) and dimensionless velocity shear λ=(UX2 - UX1) / (UX2 + UX1) where UX1 and UX2 are two flow velocities characterizing the low-speed stream and high-speed stream, respectively. Two flow depths were tested, with the λ-value at the flume entrance varying between 0.1 to 0.8, with a threshold value λ = 0.3 needed for the emergence of KHCSs in compound open-channel flows being inside this range. This paper reports new data that provide a better insight in the interplay between the constraining effect of flow depth, damping effect of three-dimensional bed-induced turbulence, and triggering effect of dimensionless shear on the formation of KHCSs.

Original languageEnglish
Title of host publicationRiver Flow 2020 - Proceedings of the 10th Conference on Fluvial Hydraulics
EditorsWim Uijttewaal, Mario J. Franca, Daniel Valero, Victor Chavarrias, Claudia Ylla Arbos, Ralph Schielen, Ralph Schielen, Alessandra Crosato
PublisherCRC Press/Balkema
Number of pages8
ISBN (Electronic)9780367627737
Publication statusPublished - 2020
Event10th Conference on Fluvial Hydraulics, River Flow 2020 - Virtual, Online, Netherlands
Duration: 7 Jul 202010 Jul 2020


Conference10th Conference on Fluvial Hydraulics, River Flow 2020
CityVirtual, Online


  • Coherent structures
  • Shallow shear flows
  • Shear layer turbulence


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