Cross-sectional flow and velocity redistribution in a meandering laboratory flume

Abstract

The role played by the cross-stream circulation could be important in the longitudinal flow velocity and bed shear stress redistributions, which determine the bed topography (Blanckaert et al., 2008). Recent experimental results obtained in a strongly curved channel (Blanckaert and Graf, 2001) and in a large amplitude meandering flume (Termini and Piraino, 2011) have highlighted that, besides the main central-region cell, a counter-rotating secondary circulation cell forms near the outer bank along the curved reaches of the channel. In this context, the present work aims at improving the understanding of the flow characteristics along a meandering bend. The analysis is based on detailed velocity data set collected in a large amplitude meandering laboratory flume. In previous works (see as an example Termini and Piraino, 2011) the data were used to analyze the evolution of the secondary circulation motion along the flume; particular attention was focused on the outer bank zone, where erosion occurs. As results, it was observed that the outer-bank region circulation cell initiates at the bend entrance assuming at the apex section its complete development. In this work, attention is paid to the role played by the cross-sectional circulation motion on the redistribution of longitudinal flow velocity. The evolution of the advective momentum transport by cross-circulation motion is analyzed and the influence of geometric parameters on the entity of the advective momentum transport is investigated. This allows gain of insight in the feedback between the momentum transport by cross-circulation and the downstream velocity in a large-amplitude meandering channel.