Hydraulic design aspects for supercritical flow in vortex drop shafts

ABSTRACT

Vortex drop shafts, as special sewer manholes, operate optimally if an adequate energy dissipation is guaranteed and the integrity of the structural components is safeguarded. The results of an experimental study on a vortex drop shaft with supercritical inflow are discussed herein. The hydraulic behaviour of the spiral inlet, the vertical shaft and the dissipation chamber is described. Based on detailed flow observations, useful recommendations for designing these structures are provided. It is demonstrated that a relation adopted for supercritical bend flows provides a reliable estimation of the maximum wave height along the inlet. A procedure for predicting the rotational flow angles and the velocity distribution along vertical shafts with swirling flows is developed. Water levels and pressure measurements in the dissipation chamber are further analysed to identify maximum forces acting on the chamber invert and to derive preliminary design equations.

KEYWORDS:

• Dissipation chamber
• energy dissipation
• physical model
• sewer manhole
• supercritical flow
• vortex drop shaft

Acknowledgements

The support of the municipality of Cossonay and of the Laboratory of Hydraulic Structures (LCH) of École Polytechnique Fédérale de Lausanne (EPFL), where the experiments were conducted, is sincerely appreciated. In addition, Gaetano Crispino acknowledges the funding program “VALERE” (2018) by Università della Campania Luigi Vanvitelli, which supported his research.

Disclosure statement

No potential conflict of interest was reported by the authors.