Fully Resolved Simulations of Stationary Particles in Turbulent Flow

Gas flows containing a dilute loading of solid particle 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. Many numerical models implicitly assume that the particles are significantly smaller than all turbulence length scales. Simple particle drag laws derived 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 the gas phase in order 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 flow Kolmogorov scale, η. Here we perform fully-resolved simulations of a fixed particle in decaying homogeneous isotropic turbulence using an overset grid method. All flow scales are accurately resolved with this technique including the effect of the no-slip boundary condition at the particle surface. A set of 29 simulations with an initial Taylor microscale Reynolds number, Re_λ = 32.2, and Kolmogorov length scale, η = 0.45d are computed to obtain a useful statistical sample. The turbulent kinetic energy and viscous dissipation near the particle surface in laden and unladen simulations are compared to provide understanding of the turbulence modification process. We anticipate that these results will provide direction for the development of turbulence modification models suitable for larger scale simulations where the flow cannot be resolved to the particle surface.