Study of the shear stress in narrow channels: application to sewers

Abstract

The management of deposits in combined sewers is of vital importance from a technical and management point of view. In combined sewers, there are a wide range of shape of cross-sections that have not been characterised from a hydraulic aspect and where it is difficult to measure accurately the near wall velocity and shear stress. A research programme, therefore, is in progress to study how flows behave in such channels and the numerical simulations can be used systematically to investigate some parameters viz. velocity field, shear stress. In the present study, a numerical method was employed to compute distribution of shear stress in whole of the cross sections. The effect of turbulence modelling in simple and combined cross section was investigated. A comparison between one-dimensional and three-dimensional flow equations was carried out to estimate distribution of the shear stress. The three-dimensional model results were in close agreement with experimental data, whereas one-dimensional equations could not fit with experimental values.

Keywords:

• narrow channels
• secondary currents
• sewer
• wall shear stress

Acknowledgements

This work has been supported by GEMCEA, a Public Interest Group for Assessing Measurements for Water and Sewerage. The authors wish to acknowledge the technical staffs of both the Laboratoire Central des Ponts et Chaussées Division Eau & Environnement and the Direction de l'Assainissement de la Communauté Urbaine de Nantes (Nantes Wastewater Authority) for their valuable contributions to these experiments.