Near-bed turbulence around an unsubmerged L-head groyne

Abstract

ABSTRACT L-head groynes are widely used in river training, thereby motivating the present study of the near-bed turbulence around an unsubmerged L-head groyne. Near-bed turbulence characteristics are required to understand the fluctuations of turbulent structures to ensure the safety of such groynes for bank protection work. In this study, the mean and turbulent flow characteristics such as time-averaged three-dimensional velocity distribution, Reynolds stresses, turbulent kinetic energy, and bed shear stress have been investigated experimentally at a channel Reynolds number of 3.9 × 104 and Froude number of 0.34. The maximum positive streamwise velocity along detached shear layer (DSL) and negative velocity within the wake zone are found as 1.51 and 0.60 times the mean flow velocity, respectively. Amplified transverse velocity caused by horseshoe vortex and the increased vertical velocity caused by downflow are observed in the upstream recirculation region. From the Reynolds stress variation, stronger horizontal turbulent mixing than the vertical turbulent mixing is observed. Amplified normal stresses and kinetic energy are observed along the DSL, which represents the intense turbulent fluctuations because of the presence of high shear instability therein. The bed shear stress at the junction of the groyne faces increases by 4.78 times the approach bed shear stress.