CFD Modeling of a Hydrodynamic Separator

Particle dynamics in a hydrodynamic separator subject to transient rainfall‐runoff

“…Previous studies in modeling swirling multiphase flows in hydrocyclones have employed two equation Reynolds averaged Navier‐Stokes (RANS) models including the standard k ‐ɛ model for turbulence modeling of hydrocyclones [ Nowakowski et al , 2004; Statie et al , 2001; Petty and Parks , 2001]. The standard k ‐ɛ model was used to successfully model steady flow as part of a previous study and supported with validation data for a screened HS under controlled steady testing [ Pathapati and Sansalone , 2009]. The realizable k ‐ɛ model was tested in this study and was found to offer no improvement over the standard k ‐ɛ model.…”

“…The behavior of the screened HS is modeled more accurately in three dimensions because of the simultaneous effects of lack of geometric symmetry, complex static screen geometry, vortex flow and gravitational forces on the motion of particles. The fluid flow equations solved by CFD are based on conservation of mass and momentum [ Versteeg and Malalasekera , 1995] with details of these equations for the HS provided elsewhere [ Pathapati and Sansalone , 2009].…”

“…The screen area open to flow is designed so that radial velocity through the screen is approximately an order of magnitude lower than the inlet velocity. The screen was modeled as a momentum sink term, and the detailed methodology is provided elsewhere [ Pathapati and Sansalone , 2009].…”

“…The measured influent particles were numerically injected at times that correspond to influent sampling times during storm event data collection. The Lagrangian DPM is derived from force balances based on Newton's law describing particle settling [ Pathapati and Sansalone , 2009]: In this expression, In these expressions, u is fluid velocity, u p is particle velocity, ρ is fluid density, ρ p is particle density, d p is particle diameter, μ is viscosity, a 1 , a 2 , a 3 are empirical constants for spherical particles as a function of the particle Reynolds number, Re p [ Morsi and Alexander , 1972].…”

“…The application of a CFD to model PM‐laden flows is an active research area [ Curtis and van Wachem , 2004; van Wachem and Almstedt , 2003]. Pathapati and Sansalone [2007, 2009] developed an experimentally validated CFD approach to accurately describe behavior of a screened HS, across a range of steady flow rates for an influent of constant PSD at a constant concentration (EMC) typically observed in urban rainfall‐runoff. This study extends the CFD modeling to unsteady rainfall‐runoff events with transient flow rates, and variable but flow‐coupled influent PSDs and PM concentrations.…”