Spectral shortcut in turbulence energy transfer in open channel flow over submerged vegetation

摘要

This study explores the characteristics of the spectral shortcut in the turbulence kinetic energy transfer in experimental open channel flows with the presence of submerged vegetation flow. The vegetation layer was simulated by arrays of rigid vertical cylinders, distributed uniformly in the channel bed. Results indicate that there are dual inertial subranges (ISRs) in the spectral distribution of turbulence energy in the penetration layer, where the Kelvin-Helmholtz (KH) and wake vortices coexist. The lower-frequency and higher-frequency ISRs reflect the energy cascading of the KH and wake-scale vortices, respectively. Spectral shortcut narrows the ISR for the KH vortex and contributes to the ISR for the wake-scale vortices, because such an action transfers a significant amount of turbulent energy directly from the large-scale eddies to the wake-scale vortices. We study the influence of spectral shortcut on energy transfer according to the turbulence kinetic energy budget equation for shear turbulence. The transferred energy is found to account for 58-71% of the shear turbulent energy and contributes considerably to the wake-scale turbulence. The strength of the energy transfer increases with the increase in the vegetation density and the mean bulk velocity and the decrease in the relative submergence.