Subgrid simulations of reacting two-phase shear layers

A two-phase subgrid combustion model has been developed for large-eddy simulations (LES). This approach includes a more fundamental treatment of the effects of the final stages of droplet vaporization, molecular diffusion, chemical reactions and small scale turbulent mixing than other LES closure techniques. In the present approach, the liquid droplets are tracked using the Lagrangian approach up to a pre-specified cut-off size. The phase change of the droplets both larger and smaller than the cut-off size and the subsequent mixing of the evaporated fuel with the oxidizer are modeled within the subgrid using an Eulerian two-phase model. It is shown here that the present approach gives consistently better results for both infinite and finite-rate kinetics in turbulent mixing layer even when the cut-off is increased. In contrast, conventional LES under similar conditions result in significant error when the cut-off size is increased. Finally, as a prelude to the study reacting sprays in realistic gas turbine combustors, a spatially evolving co-axial spray configuration is simulated using a new parallel LES version of the present model. Results are analyzed and discussed to demonstrate the new capability that has been developed

On LEM/LES methodology for two-phase flows

A two-phase subgrid combustion model developed earlier has been evaluated for applicability in large-eddy 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

Numerical simulation and validation of dilute turbulent gas-particle flow with inelastic collisions and turbulence modulation

This work describes a theoretical and numerical study of turbulent gas-particle flows in the Eulerian framework. The equations describing the flow are derived employing Favre averaging. The closures required for the equations describing the particulate phase are derived from the kinetic theory of granular flow. The kinetic theory proposed originally is extended to incorporate the effects of the continuous fluid on the particulate phase behavior. Models describing the coupling between the continuous phase kinetic energy and particulate phase granular temperature are derived, discussed, and their effect on the flow predictions is shown. The derived models are validated with benchmark experimental results of a fully developed turbulent gas-solid flow in a vertical pipe. The effect of the models describing the influence of turbulence on the particle motion as well as the turbulence modulation due to the presence of particles is analyzed and discussed