Modelling Stilling Basins for Sewage Networks

Abstract

Concrete elements play an effective role in stilling basin design in terms of enhancing the dissipation of energy to prevent immoderate scouring of downstream structures. Proper appurtenances, such as wedge-shaped splitter blocks, baffle walls, inverted t-sections, rectangular walls, inverted L sections, and impact walls, are thus utilised with circular pipe outlets to create stilling basins that are shorter yet more effective, and thus more economical. This research was based on numerical analysis of stilling basins using FLOW-3D software; the resulting Froude numbers were compared with the Froude number of a case study, a stilling basin manhole created by the Karbala Government. This research thus examined the influence of Froude number, the arrangement and location of dissipators, and the height of the pipe inlet under different hydraulic condition in order to better simulate stilling basin models. The turbulent energy dissipation was found to vary from 16% to 85%. The results from the models showed that L-sections offered maximum turbulent energy dissipation (ΔE/E1), while the rectangular wall shape gave minimum turbulent energy dissipation (ΔE/E1). It was also observed that the maximum turbulent kinetic energy almost always occurred in the initial sections, with flow becoming generally less turbulent at the end sections. Thus, at the end of all stilling basins, the turbulent kinetic energy dissipation and turbulent kinetic energy profiles became more uniform. The proposed numerical simulation using FLOW-3D was shown to be a reliable tool for predicting and discussing the turbulent energy dissipation in stilling basins. Further conclusions included the fact that the maximum turbulent energy dissipation (ΔE/E1) increases as values of Fr increase. The results of this research could thus help hydraulic designers to consider their selections for the optimum design of stilling basins more carefully.