On LEM/LES Methodology for Two-Phase Flows

A two-phase subgrid combustion model developed earlier has been evaluated for applicability in largeeddy simulations (LES). Direct Numerical Simulations (DNS) of two-phase isotropic turbulence in the presence of passive, momentum-coupled and vaporizing droplets has been extensively studied to form a base-line database. Current DNS results agree with earlier studies and show that the presence of droplets increase the kinetic energy and dissipation at the small scales. LES for these same cases were also carried out to investigate what modifications are needed to incorporate the small-scale turbulence modifications seen in DNS of two-phase flows. LES subgrid modeling for two-phase mixing within the context of the new subgrid combustion model is also addressed. INTRODUCTION Liquid fuel is used in many of the conventional engines (e.g., gas-turbine, internal combustion and diesel engines). Environmental concerns, government regulations and commercial viability makes it imperative to increase efficiency and reduce emissions. To achieve these desired features, there is a need to develop numerical methods which can accurately capture liquid fuel atomization process and fuel-air mixing downstream of the fuel injector. Steady-state methods are not suitable for studying highly unsteady fuel atomization and fuel-air mixing processes. On the other hand, although the unsteady mixing process can be studied quite accurately using direct numerical simulation (DNS) (e.g., Poinsot, 1996), the application of DNS is limited to low to moderate Reynolds numbers (Re) due to resolution requirements and t. Currently at Oak Ridge National Labs, Oak Ridge, TN. $. Professor, Senior Membk, AIAA * Copyright