Structure of a particle-laden round jet

Longmire, Ellen; Eaton, John K.

doi:10.1017/s002211209200140x

Cited by 323 publications

(117 citation statements)

References 7 publications

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“…They traced the particles backwards in time and found that the most highly dispersed particles originated from inclined narrow bands within the braid regions. Their results also support previous findings by several of the above investigators, as well as by Wen et al (1992), Longmire & Eaton (1992) (for a jet), Kiger & Lasheras (1995, confirming the existence of particle concentration 'streaks' forming in braid regions between spanwise vortices (see also Crowe, Troutt & Chung 1995). In a related issue, Kiger & Lasheras (1995) found that the vortex pairing process has a homogenizing effect on the particle distribution.…”

Section: Introductionsupporting

confidence: 88%

Direct numerical simulation of a confined three-dimensional gas mixing layer with one evaporating hydrocarbon-droplet-laden stream

Miller¹,

1999

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Direct numerical simulations are performed of a confined three-dimensional, temporally developing, initially isothermal gas mixing layer with one stream laden with as many as 7.3×10 5 evaporating hydrocarbon droplets, at moderate gas temperature and subsonic Mach number. Complete two-way phase couplings of mass, momentum and energy are incorporated which are based on a thermodynamically self-consistent specification of the vapour enthalpy, internal energy and latent heat of vaporization. Effects of the initial liquid mass loading ratio (ML), initial Stokes number (St 0 ), initial droplet temperature and flow three-dimensionality on the mixing layer growth and development are discussed. The dominant parameter governing flow modulation is found to be the liquid mass loading ratio. Variations in the initial Stokes number over the range 0.5 6 St 0 6 2.0 do not cause significant modulations of either first-or second-order gas phase statistics. The mixing layer growth rate and kinetic energy are increasingly attenuated for increasing liquid loadings in the range 0 6 ML 6 0.35. The laden stream becomes saturated before evaporation is completed for all but the smallest liquid loadings owing to: (i) latent heat effects which reduce the gas temperature, and (ii) build up of the evaporated vapour mass fraction. However, droplets continue to be entrained into the layer where they evaporate owing to contact with the relatively higher-temperature vapour-free gas stream. The droplets within the layer are observed to be centrifuged out of high-vorticity regions and to migrate towards high-strain regions of the flow. This results in the formation of concentration streaks in spanwise braid regions which are wrapped around the periphery of secondary streamwise vortices. Persistent regions of positive and negative slip velocity and slip temperature are identified. The velocity component variances in both the streamwise and spanwise directions are found to be larger for the droplets than for the gas phase on the unladen stream side of the layer; however, the cross-stream velocity and temperature variances are larger for the gas. Finally, both the mean streamwise gas velocity and droplet number density profiles are observed to coincide for all ML when the cross-stream coordinate is normalized by the instantaneous vorticity thickness; however, first-order thermodynamic profiles do not coincide.

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Section: Introductionsupporting

confidence: 88%

Direct numerical simulation of a confined three-dimensional gas mixing layer with one evaporating hydrocarbon-droplet-laden stream

Miller¹,

1999

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“…Experimental evidence for these preferential-concentration effects has been reported in earlier work (see for instance Longmire & Eaton 1992). In this scenario, the droplets cross the mixing layer to vaporize on the other side surrounded by hot air.…”

Section: Droplet Dispersion and Ignition In Turbulent Mixing Layersmentioning

confidence: 54%

“…2) the parameter controlling the overall dispersion characteristics in particle-laden turbulent mixing layers (Longmire & Eaton 1992). Different values of St are associated with different regimes of droplet dispersion, as depicted in figure 2 (a-c).…”

Section: Droplet Dispersion and Ignition In Turbulent Mixing Layersmentioning

confidence: 99%

Dynamics of thermal ignition of spray flames in mixing layers

et al. 2013

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Conditions are identified under which analyses of laminar mixing layers can shed light on aspects of turbulent spray combustion. With this in mind, laminar spray-combustion models are formulated for both non-premixed and partially premixed systems. The laminar mixing layer separating a hot-air stream from a monodisperse spray carried by either an inert gas or air is investigated numerically and analytically in an effort to increase understanding of the ignition process leading to stabilization of high-speed spray combustion. The problem is formulated in an Eulerian framework, with the conservation equations written in the boundary-layer approximation and with a one-step Arrhenius model adopted for the chemistry description. The numerical integrations unveil two different types of ignition behaviour depending on the fuel availability in the reaction kernel, which in turn depends on the rates of droplet vaporization and fuel-vapour diffusion. When sufficient fuel is available near the hot boundary, as occurs when the thermochemical properties of heptane are employed for the fuel in the integrations, combustion is established through a precipitous temperature increase at a well-defined thermal-runaway location, a phenomenon that is amenable to a theoretical analysis based on activation-energy asymptotics, presented here, following earlier ideas developed in describing unsteady gaseous ignition in mixing layers. By way of contrast, when the amount of fuel vapour reaching the hot boundary is small, as is observed in the computations employing the thermochemical properties of methanol, the incipient chemical reaction gives rise to a slowly developing lean deflagration that consumes the available fuel as it propagates across the mixing layer towards the spray. The flame structure that develops downstream from the ignition point depends on the fuel considered and also on the spray carrier gas, with fuel sprays carried by air displaying either a lean deflagration bounding a region of distributed reaction or a distinct double-flame structure with a rich premixed flame on the spray side and a diffusion flame on the air side. Results are calculated for the distributions of mixture fraction and scalar dissipation rate across the mixing layer that reveal complexities that serve to identify differences between spray-flamelet and gaseous-flamelet problems.

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“…In other shear dominated flows particle centrifuging was also found. For example Longmire & Eaton (1992) used phase-locked digital imaging to measure the spatial distribution of particle number density in a pulsed jet laden with glass beads. They found that the instantaneous number density, integrated radially over the jet, had maximum values up to three times larger than the minimum values.…”

Section: Introductionmentioning

confidence: 99%