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Direct numerical simulation of a transitional temporal mixing layer laden with multicomponent-fuel evaporating drops using continuous thermodynamics

Le Clercq, P. C. and Bellan, J. (2004) Direct numerical simulation of a transitional temporal mixing layer laden with multicomponent-fuel evaporating drops using continuous thermodynamics. Physics of Fluids, 16 (6). pp. 1884-1907. ISSN 1070-6631. http://resolver.caltech.edu/CaltechAUTHORS:LECpof04

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Abstract

A model of a temporal three-dimensional mixing layer laden with fuel drops of a liquid containing a large number of species is derived. The fuel model is based on continuous thermodynamics, whereby the composition is statistically described through a distribution function parametrized on the species molar weight. The drop temperature is initially lower than that of the carrier gas, leading to drop heat up and evaporation. The model describing the changes in the multicomponent (MC) fuel drop composition and in the gas phase composition due to evaporation encompasses only two more conservation equations when compared with the equivalent single-component (SC) fuel formulation. Single drop results of a MC fuel having a sharply peaked distribution are shown to compare favorably with a validated SC-fuel drop simulation. Then, single drop comparisons are performed between results from MC fuel and a representative SC fuel used as a surrogate of the MC fuel. Further, two mixing layer simulations are conducted with a MC fuel and they are compared to representative SC-fuel simulations conducted elsewhere. Examination of the results shows that although the global layer characteristics are generally similar in the SC and MC situations, the MC layers display a higher momentum-thickness-based Reynolds number at transition. Vorticity analysis shows that the SC layers exhibit larger vortical activity than their MC counterpart. An examination of the drop organization at transition shows more structure and an increased drop-number density for MC simulations in regions of moderate and high strain. These results are primarily attributed to the slower evaporation of MC-fuel drops than of their SC counterpart. This slower evaporation is due to the lower volatility of the higher molar weight species, and also to condensation of already-evaporated species on drops that are transported in regions of different gas composition. The more volatile species released in the gas phase earlier during the drop lifetime reside in the lower stream while intermediary molar weight species, which egress after the drops are entrained in the mixing layer, reside in the mixing layer and form there a very heterogeneous mixture; the heavier species that evaporate later during the drop lifetime tend to reside in regions of high drop number density. This leads to a segregation of species in the gas phase based on the relative evaporation time from the drops. The ensemble-average drop temperature becomes eventually larger/smaller than the initial drop temperature in MC/SC simulations. Neither this species segregation nor the drop temperature variation with respect to the initial temperature or as a function of the mass loading can be captured by the SC-fuel simulations.


Item Type:Article
Additional Information:©2004 American Institute of Physics. (Received 15 September 2003; accepted 29 January 2004; published online 28 April 2004) This research was performed at the Jet Propulsion Laboratory (JPL) of the California Institute of Technology, under the partial sponsorship of the Donors of The Petroleum Research Fund, administered by the American Chemical Society. Additional sponsorship was provided by U.S. Department of Energy (DOE) with Neil Rossmeissl (DOE Headquarters) and D. Hooker (DOE Golden Center) serving as contract monitors, under an agreement with the National Aeronautics and Space Administration. The authors wish to thank Dr. Kenneth Harstad of JPL for many helpful discussions on thermodynamics and Dr. Nora Okong’o of JPL for help with numerical and computational aspects. Computational resources were provided by the supercomputing facility at JPL.
Subject Keywords:drops; numerical analysis; flow simulation; mixing; evaporation; fuel; two-phase flow; vortices; thermodynamics
Record Number:CaltechAUTHORS:LECpof04
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:LECpof04
Alternative URL:http://dx.doi.org/10.1063/1.1688327
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1885
Collection:CaltechAUTHORS
Deposited By: Archive Administrator
Deposited On:22 Feb 2006
Last Modified:26 Dec 2012 08:46

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