(25c) Quantification of Gas–Phase Velocity Fluctuations In Statistically Homogeneous Gas–Solid Flow Using Particle–Resolved Direct Numerical Simulation

Gas–phase velocity fluctuations in statistically homogeneous gas–solids flow are quantified using particle–resolved direct numerical simulation (DNS). The kinetic energy associated with the gas–phase velocity fluctuations k_f in steady flow past fixed random assemblies of monodisperse spheres is characterized as a function of solid volume fraction φ and the Reynolds number based on the mean slip velocity Re_m. The DNS approach is based on a new formulation we refer to as the  Particle–resolved Uncontaminated–fluid Reconcilable Immersed Boundary Method (PUReIBM). A simple scaling analysis is used to explain the dependence of k_f on φ and Re_m. The steady value of k_f results from the balance between the source of k_f due to interphase transfer of kinetic energy, and the dissipation of k_f in the gas–phase. It is found that it is appropriate to model the dissipation of k_f in gas–solid flows using a length scale that is analogous to the Taylor microscale used in single–phase turbulence.