ABSTRACT
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.
