Turbulent Flow and Dispersion of Inertial Particles in a Confined Jet Issued by a Long Cylindrical Pipe

Abstract

In this work we examine first the flow field of a confined jet produced by a turbulent flow in a long cylindrical pipe issuing in an abrupt angle diffuser. Second, we examine the dispersion of inertial micro-particles entrained by the turbulent flow. Specifically, we examine how the particle dispersion field evolves in the multiscale flow generated by the interactions between the large-scale structures, which are geometry dependent, with the smaller turbulent scales issued by the pipe which are advected downstream. We use Large-Eddy-Simulation (LES) for the flow field and Lagrangian tracking for particle dispersion. The complex shape of the domain is modelled using the immersed-boundaries method. Fully developed turbulence inlet conditions are derived from an independent LES of a spatially periodic cylindrical pipe flow. The flow field is analyzed in terms of local velocity signals to determine spatial coherence and decay rate of the coherent K-H vortices and to make quantitative comparisons with experimental data on free jets. Particle dispersion is analyzed in terms of statistical quantities and also with reference to the dynamics of the coherent Flow Turbulence Combust (2009) 82:1-23 structures. Results show that the particle dynamics is initially dominated by the Kelvin-Helmholtz (K-H) rolls which form at the expansion and only eventually by the advected smaller turbulence scales.

Effects of the Turbulent-to-Laminar Transition in Monolithic Reactors for Automotive Pollution Control

“…The dispersion of inertial diesel soot particles in an axisymmetric diffuser was investigated in great detail by Sbrizzai et al The large particles considered in the current work (species C) are still small enough to respond to all scales of fluid motion, i.e., both the instabilities caused by the diffuser and the turbulent fluctuations from upstream the diffuser. Consequently, Sbrizzai et al also showed that such particles are quickly dispersed by the combined action of small and large flow structures . We can thus conclude that it is reasonable to use a uniform particle distribution at the inlet in the numerical simulations in the current work.…”

“…In other words, we neglect any additional large-scale turbulent structures upstream the reactor arising from the typical enlargement of the exhaust pipe to fit a monolith of larger diameter. These structures have been the focus of earlier studies, − and the influence of this assumption is discussed in detail later in this paper.…”

“…It should be noted here that the quantitative results from the current work most probably will be influenced by the choice of turbulent inlet conditions, and that the actual turbulence characteristics in a real application are a complex function of the geometry and operating conditions. Most notably, the presence of large-scale structures generated by an upstream diffuser (not taken into account in the current work) could cause clustering of inertial particles . A detailed discussion about the influence of the values of k and ε chosen in the current work is therefore presented after the results.…”

“…The investigation is done by solving for the actual flow field using a large eddy simulation (LES) and by estimating the conversion of a number of common pollutants under the assumption that the conversion is mass transfer limited (i.e., that the ratio of the wall concentration to the average radial concentration of a reactant species is less than 0.03) . Although the effects of soot particle dispersion in a diffuser upstream a monolithic reactor have been investigated before, , this isto our knowledgethe first attempt of an in-depth study of turbulent-to-laminar transition effects at the inlet of a monolithic reactor.…”

Inflow turbulence generation techniques for large eddy simulation of flow and dispersion around a model building in a turbulent atmospheric boundary layer

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