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
Subtitle of host publicationProceedings of the 10th Conference on Fluvial Hydraulics (Delft, Netherlands, 7-10 July 2020)
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 - 10 Jul 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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