Turbulent Multiphase Flows
Recent measurements and predictions concerning turbulent multiphase flows are considered, emphasizing findings of the author and his associates. The properties of both dense sprays (comparable phase volume fractions) and dilute dispersed multiphase flows (dispersed-phase volume fractions less than 1–10 percent) are considered.
Results for dense sprays are limited to the near-injector region of noncombusting, combusting monopropellant, and combusting bipropellant sprays from pressure-atomizing injectors. The results suggest that these flows approximate locally-homogeneous flow properties in the atomization regime, but exhibit much slower mixing rates as the first wind-induced breakup regime is approached, in a manner which is not anticipated by predictions. Flow properties for the atomization regime are strongly influenced by the degree of flow development and turbulence levels at the injector exit. However, existing measurements of the structure of dense sprays are very limited: more work is required to assess the appropriate flow regimes and the effectiveness of locally homogeneous flow analysis for these flows.
Contemporary stochastic analysis of dilute multiphase flows has provided encouraging predictions of the mean structure and mixing properties (turbulent dispersion) of a variety of dilute dispersed flows. However, effects of turbulence modulation (the modification of turbulence properties by the dispersed phase) have been observed, which existing theoretical methods cannot treat effectively, due to inadequate consideration of the response of the dispersed phase to various wave numbers of the turbulence spectrum. Interphase transport phenomena associated with high relative turbulence intensities, virtual mass forces, Basset history forces, and the existence of envelope flames around drops, are also not sufficiently understood to provide reliable predictions of the properties of the dilute portions of combusting sprays.
KeywordsMixture Fraction Slug Flow Turbulence Modulation Turbulent Dispersion Liquid Volume Fraction
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