(458c) Modeling Dilute Gas-Solid Turbulent Flows Using Moment Methods

Numerical simulation offers a powerful tool for modeling particle-fluid interactions in turbulent two-phase flows.  Although Lagrangian particle-tracking methods are a plausibly accurate approach, these models are often limited to dilute flows and can be inaccurate in regions of locally large particle concentrations where inter-particle interactions and effects of two-way coupling can be significant.   These and other considerations motivate the current effort aimed at implementing Eulerian-based approaches that treat the particle phase as a continuum.  The specific focus of the current effort is on modeling dilute particle-laden turbulence in which the gas-phase carrier flow is populated with a second phase of small, dispersed solid particles possessing material densities much larger than that of the carrier flow, and consequently large particle Stokes numbers.  The approach adopted in this work is derived from the quadrature-based method of moments (QMOM) developed originally by McGraw (1997), and is known as the conditional QMOM method (CQMOM) developed by Yuan and Fox (2011).

Simulations are conducted of a particle-laden turbulent boundary layer, both with and without a coherent vortex periodically introduced into the flow that distorts the boundary layer. The gas-phase carrier flow is computed using Direct Numerical Simulation of the incompressible Navier-Stokes equations. The dispersed solid phase is coupled to the fluid via a drag force acting on the particles and modeled using CQMOM.  The boundary layer develops spatially from a turbulent inflow condition; in cases in which the coherent vortex is used to distort the flow, the vortex impinges into the boundary layer around 20 initial boundary layer thicknesses downstream of the inlet. The simulations show that the carrier flow drives the particulate phase via the drag force and with resulting structural interactions, e.g., preferential concentration of particles, similar to those observed in Lagrangian particle tracking simulations.  Further comparisons are made against simulations using Lagrangian particle tracking of the dispersed phase and demonstrate the utility of the Eulerian approach, e.g., with statistical descriptors in reasonable agreement between the two methods. Instantaneous and time-averaged statistics are presented, as well as phase-averages for the cases involving time-periodic impinging vortices.