Numerical study of the near-wall behaviour of particles in turbulent pipe flows

• Published in: Powder technology Vol. 125; no. 2; pp. 149 - 157
• Main Authors: Portela, Luı́s M, Cota, Pierpaolo, Oliemans, René V.A
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Lausanne Elsevier B.V 11.06.2002; Elsevier
• Subjects: Computational methods in fluid dynamics; Direct numerical simulation; Exact sciences and technology; Fluid dynamics; Fundamental areas of phenomenology (including applications); Multiphase and particle-laden flows; Near wall; Nonhomogeneous flows; Particles; Physics; Turbulent pipe flow; Turbulent pipe flow; Direct numerical simulation; Near wall; Particles; Phase velocity; Turbulent flow; Pipe flow; Two-phase flow; Digital simulation; Wall effects; Spherical particle; Particle suspension; Finite volume methods; Concentration distribution
• ISSN: 0032-5910; 1873-328X
• DOI: 10.1016/S0032-5910(01)00501-0

The near-wall behaviour of particles is important in terms of predicting both the particle-deposition and the near-wall particle-concentration. In this paper, we study the near-wall behaviour of elastic-bouncing small heavy spheric particles in fully developed turbulent pipe flows without gravity, using direct numerical simulations (DNS) with a one-way point-particle approach. The particle-concentration is assumed to be small enough such that the influence of the particles on the fluid and interparticle interactions can be neglected. The focus of the paper is on: (i) the understanding of the differences between elastic-bouncing and absorbing walls, and (ii) the evaluation of simple “local-equilibrium” models. Our results show that the near-wall behaviour of elastic-bouncing walls is very different from absorbing walls. The absence of a mean radial particle-velocity leads to a much higher particle-concentration near the wall than in the case of absorbing walls. This can be explained by the absence of a “mean drag force”: the “turbophoretic effect”, due to the gradient in the particle-velocity fluctuation in the radial direction, is balanced only by the “drift-velocity”, due to a gradient in the particle-concentration. Our results indicate that, from a pragmatic perspective, simple “local-equilibrium” models for the “turbophoretic effect”, assuming a proportionality between the particle and fluid “Reynolds-stresses”, are adequate, except very close to the wall, where the reduction in the radial fluid-velocity fluctuation is not accompanied by an equivalent reduction in the radial particle-velocity fluctuation.