Conditional spatially averaged flow statistics in a rigid, submerged vegetated environment

In submerged vegetated flows, the role of coherent flow structures, in terms of conditional statistics, induced by the shear layer in fluid mixing remains not fully understood. This study examines the conditional turbulence and dispersive quantities in a rigid, submerged vegetated flow. A laboratory experiment was conducted, and three-dimensional velocity data were collected using an acoustic Doppler velocimeter system. All conditional spatially averaged (SA) streamwise velocity distributions exhibit a distinct inflection at the canopy top, with sweeps showing the highest magnitude and ejections the lowest across the flow depth. At the canopy top, their contributions vary by over 30% from the total streamwise velocity. Conditional analysis of SA Reynolds normal and shear stresses and turbulent kinetic energy fluxes shows that ejections are to enhance momentum and energy fluxes above the canopy top, while sweeps play the dominant role within the canopy. At the canopy interface, ejections and sweeps produce more than twice the overall Reynolds shear stress. Conditional SA Reynolds normal stresses are significantly elevated near the canopy top, reflecting enhanced turbulence. Conditional analysis of dispersive normal and shear stresses and dispersive kinetic energy (DKE) fluxes further shows that dispersive ejections are the major contributors to momentum and energy redistribution within the canopy. The peak vertical DKE flux from dispersive ejections reaches 11% of its streamwise counterpart within the canopy. Additionally, the study reveals that ejections occur more frequently within the canopy, while sweeps occur more frequently above it, although ejections have longer duration across the flow depth.