On the modeling of droplet transport, dispersion and evaporation in turbulent flows
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Publication date: 2005-07-01
Combustion Engines 2005,122(3)
The present paper presents a numerical study on evaporating droplets injected through a turbulent cross-stream. Several models have been used with more or less success to describe similar phenomena, but much of the reported work deals only with sprays in stagnant surroundings. The ultimate goal of this study is to develop an Eulerian/Lagragian approach to account for turbulent transport, dispersion, evaporation and coupling between both processes in practical spray injection systems, which usually include air flows in the combustion chamber like swirl, tumble and squish in I.C. engines or crossflow in gas turbines. In this work a method developed to study isothermal turbulent dispersion is extended to the case of an array of evaporating droplets through a crossflow, and the performance of two different evaporation models widely used is investigated. The convection terms were evaluated using the hybrid or the higher order QUICK scheme. The dispersed phase was treated using a Lagrangian reference frame. The differences between the two evaporation models and its applicability to the present flow are analysed in detail. During the preheating period of the Chen and Pereira [1] model the droplets are transported far away from the injector by the crossflow, while with the Sommerfeld [2] formulation for evaporation the droplet has a continuous variation of the diameter. This result has profound implications on the results because the subsequent heat transfer and turbulent dispersion is extremely affected by the size of the particles (or droplets). As a consequence, droplet diameter, temperature and mass fraction distributions were found to be strongly dependent on the evaporation model used. So, a new formulation that takes into account also the transport of the evaporating droplets needs to be developed if practical injection systems are to be simulated. Also, in order to better evaluate and to improve the vaporization models more detailed measurements of three-dimensional configurations are required.