Numerical Assessment of Shear Boundary Layer Formation in Sewer Systems with Fluid-Sediment Phases

Yang Ho Song,Do Guen Yoo,Jin Gul Joo,Jung Ho Lee

doi:10.3390/w12051332

Yang Ho Song, Do Guen Yoo + Show 2 more

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https://doi.org/10.3390/w12051332

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Abstract

Numerical and empirical studies of soil slurry transport and deposition in urban stormwater sewers are few, presumably due to the difficulty of direct observation of soil slurry flow in stormwater pipes. Slurry in a sewer system includes both suspended load and bedload, but few studies have attempted to demarcate these two components. A boundary layer is a crucial determinant of sediment transport capacity. Stormwater runoff enters the sewer in turbulent flow, mostly mixed with soil slurry generated by rainfall. In this paper, we attempt analysis using ANSYS Fluent commercial CFD software. We describe the development of a numerical analytical methodology capable of predicting the flow of soil slurry in stormwater pipes, and propose a method for estimating the sediment–flow boundary layer. Using this model, we simulated stormwater runoff with a large content of soil slurry during a rainfall event. We investigated soil slurry transport and predict the formation of shear boundary layer by varying the inlet conditions (volume of soil slurry entering the stormwater sewer system) and by analyzing the flow velocity field and soil slurry volume fraction in the pipes under various experimental flow conditions. Based on the shear and settling velocity of sediment particles, we propose criteria for the formation of a shear boundary layer in stormwater pipes.

Highlights

South Korea’s total annual precipitation is high, but highly concentrated in the summer months, with storms producing excessively concentrated local rainfall events [1,2,3]
The deposition of a sediment layer on the bottom of the pipe is a major cause of formation of a shear deposition of a sediment layer on the bottom of the pipe is a major cause of formation of a shear boundary layer in the soil slurry transport process, and serves as a major reference point for boundary layer in the soil slurry transport process, and serves as a major reference point for
The results presented in this paper are estimations derived from the numerical analysis of various inlet conditions of soil slurry entering the stormwater sewer system

Summary

Introduction

South Korea’s total annual precipitation is high, but highly concentrated in the summer months, with storms producing excessively concentrated local rainfall events [1,2,3]. Mountainous regions affected by high rates of sediment transport often suffer damage caused by sedimentation of soils and debris in drainage pipes. Sedimentation exceeding the rate of subsidence results in overflow, increasing the risk of damage due to landslides or floods [4,5]. To prevent such damage, drainage pipe design must be informed by an understanding of flow characteristics, taking account of the sedimentation of soil and debris in the drainage network. Slurry transport through the pipeline causes various problems; for example, deposition of slurry solids lowers the performance and efficiency of the entire drainage system [6,7,8,9]

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