An implicit formulation to model the evaporation process in the Eulerian-Lagrangian Spray Atomization (ELSA) framework

An implicit evaporation model for the coherent structures of evaporating sprays was introduced and validated against experimental data of engine combustion network (ECN) spray A. The proposed method is based on a priori computation of the steady-state equilibrium conditions reached by a system composed by liquid, vapor and air at constant pressure combined with a modeled characteristic time of evaporation. Such equilibrium composition and temperature were applied inside numerical calculations to compute evaporation source terms implemented in an implicit manner. The new formulation allows simulating evaporation process in the dense zone of the spray, where, due to the extremely low time scales related to mass and heat transfer, classical explicit method usually leads to non-physical results. This innovative approach was employed in a multiphase solver based on the Eulerian–Lagrangian Spray Atomization (ELSA) model in the framework of the computational fluid dynamics suite OpenFOAM. The use of ELSA allows the mass and heat transfer terms to be modeled as a function of the transported amount of liquid–gas interface surface available for evaporation. An analysis of the model performances was performed in an URANS framework in order to highlight the physically consistent representation of evaporation phenomena of the approach in the regions characterized by a high liquid volume fraction.