Fully resolved simulations of particle-turbulence interaction

Gas flows containing a dilute loading of solid particles constitute an important class of multiphase flows. In most cases the gas flow is turbulent, and the interactions between the particles and the turbulence offer major modeling challenges. In many numerical models, simple particle drag laws for uniform steady flow around a sphere are used to compute the motion of point-particles, and to determine the magnitude of the point-forces that are applied to produce turbulence modification. This technique may be appropriate if the particle is small relative to any turbulent eddies, but in many practical problems the particle diameter, d, is of the same order as the Kolmogorov scale, &eegr;.; The development of models that are suitable for the physically relevant regime where d ∼ &eegr;, requires detailed simulations of the interaction between particles and turbulence. The first part of this work focused on the development of a numerical method suitable for performing fully resolved simulations of particle-turbulence interaction. In order to provide resolution of all length scales from the large eddies to the boundary layer at the surface of the particle, an overset grid method was chosen for these simulations. An overset grid fractional-step method was developed to solve the incompressible Navier-Stokes equations on this grid system.; The second part of this work focused on the application of the numerical scheme to particle-laden flows where d ∼ &eegr;. A set of 32 independent simulations of a fixed particle in decaying homogeneous isotropic turbulence were performed to obtain a meaningful statistical sample. Volume-averaged profiles of the turbulent kinetic energy and dissipation rate from the overset grid simulations were compared to the corresponding quantities from an unladen simulation to determine the extent of the turbulence modification by the particle. Time histories of the force applied to the particle were recorded from each overset grid simulation and compared to the forces predicted by a particle equation of motion.