Discontinuous transition in turbulence intensity in a particle-laden channel flow*

Wall bounded particulate systems exhibit various phenomena that can greatly influence the carrier phase due to dispersed phase. In the present work, the turbulence modulation of fluid phase is examined in dilute and moderately dense limit by four-way coupled Direct Numerical Simulation (DNS) in a vertically downward channel using Eulerian - Lagrangian approach. Simulation results are obtained for various Stokes number of particles. It is observed that there is a Critical Particle Volume Loading (CPVL) at which a sharp decay in turbulence intensity occurs and Reynolds stress becomes zero. The CPVL at which such a transition occurs may differ with change in Stokes number. Mean gas velocity profiles also depart from fully developed channel flow at this critical volume loading, with sharp increase at the center of the channel. Since a constant bulk flow condition is maintained, the pressure gradient and wall shear stress are modified due to particle loading. Since the Reynolds stress is zero beyond CPVL, particle feed back force balances the mean pressure gradient and viscous stress term. Mean and Turbulent Kinetic Energy (TKE)  budget for different particle loading have been estimated.