Turbulence characteristics of flow past submerged vanes

Abstract

Submerged vanes are hydrofoils utilized to manage the sediment transport through the river by generating the turbulence in the flow in the form of helical currents. The vanes are placed in the flow with respect to its direction at angle of 10o to 40o. In the current study, an attempt has been made to study the effect of the introduction of vanes in form of rows on parameters like turbulence intensities, Reynolds stresses, turbulent kinetic energy, anisotropy index, and the velocity profile of the flow. It is observed that the profile of variation of turbulence intensities, turbulent kinetic energy, vertical Reynolds stress and velocity over three different marked verticals on a transect are nearly identical whereas a large scatter is observed in the variation of transverse Reynolds stress over the vertical of the aforementioned vertical locations. This observation suggests that flow turbulence is homogeneous over the vertical while scattering in the variation of the transverse Reynolds stress component may be attributed to the presence of secondary currents in the flow. After introducing rows of submerged vanes, the bed turbulence is reduced, hence, helping reduce many scour related phenomenon. It is also observed that a vortex occurred at 0.85 times the height of the vane and the variation of turbulence quantities in the presence of vanes shows the existence of a peak in these quantities. It is observed that as flow moves away from the vane rows, due to the interaction of vortices and the action of vorticity, vortices dampens down and the flow regains homogeneity. After the introduction of submerged vane rows, bed shear stress reduces as fluid from the surface replaces the slow-moving fluid near the bed due to the secondary currents generated by the vanes leading to reduction in the magnitude of turbulence intensities, Reynolds stresses, and turbulent kinetic energy near the bed. The anisotropy index is observed to increase near the bed as induced secondary currents enhanced the turbulence production in the near bed region. All the profiles of parameters obtained in the current study show the existence of a peak or inflexions at a height of 0.85H from bed (Where, H is the height of the submerged vane). Profiles of parameters obtained in the current study suggest that as the vorticity dampens the vane-generated secondary currents, the scattering in the profiles along the vertical reduces and profiles are observed to regain the variation which they had before the introduction of vane rows, suggesting that flow turbulence has regained its homogeneity.