Entrainment and Evaporation of Drops in the Laminar Part of a Two-Dimensional Developing Mixing Layer

Abstract

A formulation has been developed that combines the simplicity of an experimentally derived well-establishedcorrelation for describing the development of a mixing layer, and a rigorous approach for the description of the dynamics and evaporation of dense or dilute clusters of drops in large coherent vortices. An extensive parametric study has been performed by varying the radius of the drops in the drop-ladenstream both for high and low air/fuel mass ratio, as well as for constant initial drop number density, but at varying air/fuel mass ratio. The air/fuel mass ratio has also been varied at fixed drop radius in the drop-laden stream. Additional parameters independently varied were the temperature of the hot air stream, its velocity, and the velocity ratio between the two streams. The results show that it is possible to optimize the relative number of drops (with respect to the initial value) entrained into the coherent vortices of the mixing layer by using the velocity ratio as control parameter. The eventual liquid mass entrained in the cluster is an increasing function of the drop radius in the drop-carrying stream for typical drop number densities in sprays. The mass fraction of the evaporated fuel in the clusters can be optimized by using the velocity of the hot air stream as a control parameter. It is also shown that, in agreement with existing observations, the average drop radius may increase withaxial distance from the mixing layer inception point, and the reasons for this are explained.

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