Enhancing Utility of Submerged Vanes with Collar

Submerged vanes are submerged foils of low height and larger length, constructed in a river at an angle of attack $\alpha$ to the flow to modify the near-bed flow pattern and redistribute flow and sediment transport within the channel cross section. At a Froude number $\left(\mathsf{F}\right)$ of 0.13, the local scour development around the submerged vane without a collar was not enough to dislodge the vane whereas at $\mathsf{F}=0.25$ , there was a significant local scour hole around the vane and the vane was dislodged. With the introduction of a collar at the leading edge of a submerged vane, the scour depth at the leading edge of the vane was reduced to zero. A collar of circular shape was found more suitable for a rectangular vane. Recommendations for sizing collars at two values of $\mathsf{F}$ are given. The optimal $\alpha$ for a rectangular vane with a collar was found close to 40°. The study clearly indicates the advantages of using collars in case of submerged vanes and provides insight into selection of appropriate collar shapes.