Obstacle-Reynolds-number based analysis of local scour at submerged cylinders

Abstract

A simple process-based, analytical approach is developed and validated herein to determine the local scour at obstacles in the fluvial environment. It is based on the obstacle Reynolds and Froude numbers. Clear-water flume experiments were conducted to investigate the local scour depths at submerged cylinders in coarse uniform sand. The resulting scour depths were correlated with an analytical model and validated with two data sets on local scour at submerged and emergent cylinders. The size of the projected frontal obstacle area in relation to the mean flow velocity has a significant effect on the scour hole shape and depth. A power law function is derived that satisfactorily describes the present scour depth data. The approach is limited to near-equilibrium clear-water scour, uniform sediment and excludes particle density effects.

Keywords:

• Local scour
• obstacle mark
• obstacle Reynolds number
• open channel flow
• submerged obstacle

Acknowledgements

The authors would like to thank two anonymous reviewers for their helpful comments as well as the DFG (Deutsche Forschungsgemeinschaft) for project funding.