Effects of the finite particle size in turbulent wall-bounded flows of dense suspensions

Abstract

We use interface-resolved simulations to study finite-size effects in turbulent channel flow of neutrally-buoyant spheres. Two cases with particle sizes differing by a factor of 2, at the same solid volume fraction of 20% and bulk Reynolds number are considered. These are complemented with two reference single-phase flows: the unladen case, and the flow of a Newtonian fluid with the effective suspension viscosity of the same mixture in the laminar regime. As recently highlighted in Costa et al. (PRL 117, 134501), a particle-wall layer is responsible for deviations of the statistics from what is observed in the continuum limit where the suspension is modeled as a Newtonian fluid with an effective viscosity. Here we investigate the fluid and particle dynamics in this layer and in the bulk. In the particle-wall layer, the near wall inhomogeneity has an influence on the suspension micro-structure over a distance proportional to the particle size. In this layer, particles have a significant (apparent) slip velocity that is reflected in the distribution of wall shear stresses. This is characterized by extreme events (both much higher and much lower than the mean). Based on these observations we provide a scaling for the particle-to-fluid apparent slip velocity as a function of the flow parameters. We also extend the flow scaling laws in to second-order Eulerian statistics in the homogeneous suspension region away from the wall. Finite-size effects in the bulk of the channel become important for larger particles, while negligible for lower-order statistics and smaller particles. Finally, we study the particle dynamics along the wall-normal direction. Our results suggest that 1-point dispersion is dominated by particle-turbulence (and not particle-particle) interactions, while differences in 2-point dispersion and collisional dynamics are consistent with a picture of shear-driven interactions.

References in corpus (9)

• An Immersed Boundary Method with Direct Forcing for the Simulation of Particulate Flows
• A collision model for grain-resolving simulations of flows over dense, mobile, polydisperse granular sediment beds
• Direct numerical simulation of pattern formation in subaqueous sediment
• The effect of particle density in turbulent channel flow laden with finite size particles in semi-dilute conditions
• Universal Scaling Laws for Dense Particle Suspensions in Turbulent Wall-Bounded Flows
• Drag reduction in turbulent channel flow laden with finite-size oblate spheroids
• Forcing homogeneous turbulence in DNS of particulate flow with interface resolution and gravity
• Turbulent channel flow of a dense binary mixture of rigid particles
• The effect of polydispersity in a turbulent channel flow laden with finite-size particles

Cited by in corpus (10)

• Interface-resolved simulations of small inertial particles in turbulent channel flow
• Exact regularized point particle (ERPP) method for particle-laden wall-bounded flows in the two-way coupling regime
• Experimental investigation of turbulent suspensions of spherical particles in a square duct
• Particle resolved simulation of sediment transport by a hybrid parallel approach
• Attenuation of turbulence in a periodic cube by finite-size spherical solid particles
• Buoyant finite-size particles in turbulent duct flow
• Turbulent channel flow of finite-size spherical particles with viscous hyper-elastic walls
• From nearly homogeneous to core-peaking suspensions: insight in suspension pipe flows using MRI and DNS
• Turbulent pipe flow with spherical particles: drag as a function of particle size and volume fraction
• Results from Particle-Resolved Simulations