Direct Numerical Simulation of Inert Droplet Effects on Scalar Dissipation Rate in Turbulent Reacting and Non-Reacting Shear Layers

Abstract

Three-dimensional direct numerical simulation has been performed to investigate the effects of inert evaporating droplets on scalar dissipation rate χ in temporally-developing turbulent reacting and non-reacting mixing layers with the Reynolds number based on the vorticity thickness up to 8000 and the number of traced Lagrangian droplets up to 10 7 . The detailed instantaneous field analysis and ensemble-averaged statistics reveal complex interactions among combustion, droplet dynamics and evaporation, all of which have a considerable influence on χ . The presence of inert evaporating droplets promotes χ in both non-reacting and reacting mixing layers. In the latter, combustion reduces χ , so when combustion is suppressed by evaporating droplets, χ is enhanced. The transport equation of χ has been analyzed to investigate the various effects on χ in detail. The terms in the equation contain explicitly the evaporation rate and its spatial derivative, acting as a sink and a source for χ , respectively. On the whole, the net effect of the evaporation-rate terms is to promote χ . However, the production and dissipation terms are the dominant source and sink terms, respectively.

Flame Structure and Propagation in Turbulent Flame-Droplet Interaction: A Direct Numerical Simulation Analysis

“…[25][26][27]. The statistical behaviour of displacement speed S d and its tangential strain rate a T and curvature κ m dependence was discussed in detail in [19] and thus the current analysis will focus next on the statistical behaviours of ∇ u, a N , a T release and the peak value is obtained at a location which is slightly skewed towards the burned gas side (i.e.…”

“…Furthermore, Re d is the droplet Reynolds number, Sc is the Schmidt number, B d is the Spalding mass transfer number, Sh c is the corrected Sherwood number and Nu c is the corrected Nusselt number, which are defined as [21,33]: The droplets are coupled to the gaseous phase via additional source terms in the gaseous transport equations, which may be generically written as [18][19][20][21][22][23][24][25][26][27][28][29][30][31]:…”

“…In recent times, both single-step [18][19][20][21][22][23][24][25][26][27][28][29] or detailed [30,31] chemistry based DNS analyses have contributed significantly to the physical understanding and modelling of the combustion of turbulent droplet-laden mixtures. In the aforementioned DNS studies, the gaseous phase is treated in a typical Eulerian fashion and the droplets are considered as sub-grid particles which are tracked in a Lagrangian manner.…”

Statistical Analysis of Turbulent Flame-Droplet Interaction: A Direct Numerical Simulation Study

“…Thus, the entire body of experimental evidence suggests that flame propagation in turbulent droplet-laden mixtures is a complex physical process depending on the simultaneous interaction of evaporative heat and mass transfer, fluid dynamics and combustion thermo-chemistry and a thorough understanding of all these phenomena will be required in order to develop accurate models for the design and development of reliable, energy-efficient engines and combustors. Direct Numerical Simulations (DNS) have contributed significantly to the physical understanding and modelling of the combustion of turbulent droplet-laden mixtures in the recent past [14][15][16][17][18][19][20][21][22][23][24][25][26], where either a single-step [14][15][16][17][18][19][20][21][22][23][24] or a detailed [25,26] chemical reaction mechanism is employed. In the aforementioned DNS studies, the gaseous phase is treated in a typical Eulerian fashion and the droplets are considered as sub-grid particles which are tracked in a Lagrangian manner.…”

Modeling Temperature Distribution Inside an Emulsion Fuel Droplet Under Convective Heating: A Key to Predicting Microexplosion and Puffing

“…Note that the "2D" here means that the axisymmetric ECME model has two independent variables R and  to model the temperature distribution inside a 3D emulsion droplet under convective heating. The cost consideration is important, because the inner-droplet temperature distribution model developed in the present study is intended to be incorporated into a Eulerian-Lagrangian code MultiPLESTaR (Xia and Luo, 2009;Xia and Luo, 2010;Xia et al, 2013) to perform high-fidelity multi-scale simulation of emulsion fuel spray processes under microexplosion/puffing conditions. In MultiPLESTaR, droplets are approximated by point particles and only one data of the double-precision kind is needed to store droplet temperature under the assumption of an infinite thermal conductivity.…”