A mixture fraction framework for the theory and modeling of droplets and sprays
- School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, NSW 2006 (Australia)
A mixture fraction is carefully defined for evaporation and combustion of droplets and sprays. The definition is valid at points in either the liquid or gas phases and care is taken to distinguish between definitions based on conserved scalars appropriate for heat transfer and those for mass transfer. Results are presented for Spalding B numbers and values of the mixture fraction at the droplet surface for the fast chemistry case and for the case where the droplet cannot sustain an envelope flame. The classical theory for an isolated droplet with spherical symmetry yields simple formulae when expressed in mixture fraction terms. New results are then readily obtained for several quantities of interest in spray modeling. The formulation provides a seamless unification of droplet evaporation processes with gas-phase mixing and reaction. Mixing in a turbulent spray jet is identified as a model problem that clarifies the role of large scale structures in the overall mixing process. Important constraints on the parameter space for sprays are shown to be greatly clarified when expressed in the mixture fraction framework. It is shown how the classical approach for segregated flow with Eulerian/Lagrangian modeling of dispersion and transfer processes in turbulent sprays can be upgraded to include fluctuations in the temperature and composition surrounding the droplets on top of those coming from the turbulent velocity fluctuations. Such preliminary calculations that assume a simple chemically reacting system can readily be upgraded using flamelet functions derived from counterflow experiments or computations: these can then form the starting point for full chemistry calculations using such approaches as conditional moment closure. (author)
- OSTI ID:
- 21401351
- Journal Information:
- Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 2 Vol. 158; ISSN CBFMAO; ISSN 0010-2180
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CALCULATION METHODS
COMBUSTION
DROPLETS
EVAPORATION
FLAMES
FLUCTUATIONS
GASES
HEAT TRANSFER
JETS
LAGRANGIAN FUNCTION
LIQUIDS
MASS TRANSFER
MIXING
MIXTURES
Mixture fraction
SCALARS
SIMULATION
SPHERICAL CONFIGURATION
SPRAYS
SURFACES
SYMMETRY
TURBULENCE
VELOCITY