Coherent turbulent structures within open-channel lateral cavities

Abstract

In the mixing layer at the interface between an open-channel flow and its adjacentlateral open-channel cavity, vortices are periodically shed and advected towards thedownstream corner. As these vortices impinge the downstream corner of the cavity,they either reach the mainstream or enter the cavity. The presence of these coherentturbulent structures within the cavity plays a major role for momentum and masstransfers between the outer layer and the core region of the recirculation cell within thecavity. Using an experimental approach based on PIV measurements and acombination of POD and coherent structure identification, we show that the vorticesentering the cavity are ad-vected by this gyre and can either travel all the way towardsthe upstream corner of or end up in the core region of this gyre. Along their trajectory,they can split in smaller vortices and/or merge with others. Moreover, while the vortexshedding in the mixing layer is highly periodic, the entering of vortices in the cavity isintermittent. Indeed, near the downstream corner of the cavity, several suc-cessivevortices can be transferred from the mixing layer to the cavity or to the mainstream. Inaver-age, the vortices are distributed almost equally between the two downstreamregions (mainstream or cavity) but we reported up to 4 successive vortices reachingthe same region.