1 © Institution of Engineers Australia, 2010 Australian Journal of Water Resources, Vol 14 No 1 * Paper W09-804 submitted 3/12/09; accepted for publication after review and revision 18/02/10. † Corresponding author Dr Monzur Imteaz can be contacted at mimteaz@swin.edu.au. CFD investigation of turbidity spikes for different velocity and particle load profles in a horizontal pipe * A Hossain, J Naser and M Imteaz † Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, Melbourne, Victoria SUMMARY: A comprehensive 3D numerical investigation of the behaviour of particles fowing through a horizontal pipe has been studied in this paper. The multiphase mixture module available in the computational fuid dynamics (CFD) model FLUENT 6.2 is used in this study. Five different time-dependent fows and particle-load profles have been used to simulate particle fow behaviour though the pipeline. The deposition of particles along the pipe has been investigated. The effect of unsteady fuid velocity over particle loads has also been investigated. Results show that after a certain length of pipe and/or travel time, when the velocity becomes steady after a deceleration period, the pipe shear stress is strong enough to cause some particle deposition or rolling along the bottom surface of the pipe wall, creating a secondary accumulation of particles (called shoot). Various velocity and particle load profles have been considered in the light of real phenomena occurring in Melbourne’s South East Water Ltd distribution network. The paper is expected to help the water authorities in understanding the propagation of turbidity spikes in pipe networks. 1 INTRODUCTION Deposition of particles from fowing suspensions is an important process in various felds of engineering and in the nature. Analysing deposition of small particles suspended in fuid streams has attracted considerable attention in the past three decades (Anderson & Russell, 1970a; 1970b; David et al, 1987; Swailes & Reeks, 1994; Thomson, 2003; Laurinat et al, 1985; Abuzeid et al, 1991; Grainger et al, 2003; Hossain et al, 2003; Hossain, 2005). This is because particle deposition plays a major role in a number of industrial processes, such as fltration, separation, particle transport, combustion, air and water pollution, and many others. Computational models for simulating the hydraulic behaviour of water-distribution systems have been available for many years (Hossain et al, 2003; Hossain, 2005; Mols & Oliemans, 1998). More recently these models have been extended to analyse water quality as well (Hossain et al, 2003; Hossain, 2005). The driving force behind this trend is the timely challenge to comply with increasingly stringent governmental regulations and customer-oriented expectations. Modern management of water distribution systems or water authorities in general need simulation models that are able to accurately predict the behaviour of particles that are responsible for turbidity spikes in the water distribution networks. Turbidity is measured in nephelometric turbidity units (NTUs), which represents the average volume scattering over a defned angular range. The greater the amount of total suspended solids in the water, the muddier it appears and the higher the measured turbidity. Large accumulation of the suspended solids produces turbidity spikes. Deposition of small particles on surfaces in turbulent fows has attracted the interest of many researchers. Using the stopping distance of a particle near a wall, Friendlander & Johnstone (1957) developed the free- fight model for particle deposition process. Davies (1966), among others, offered an improved theoretical model for particle deposition rate. Liu & Agarwal (1974) analysed the deposition of aerosol particles in turbulent pipe flows. Simplified simulation procedures for deposition of particles in turbulent fows were described by Abuzeid et al (1991) and Li & Ahmadi (1993). Mustonen et al (2008) analysed online data of water quality changes in a water distribution system.