Journal of Fluid Mechanics

Papers

Wall accumulation and spatial localization in particle-laden wall flows

G. Sardinaa1, P. Schlattera2, L. Brandta2, F. Picanoa1 and C. M. Casciolaa1 c1

a1 Dipartimento di Ingegneria Meccanica e Aerospaziale, Sapienza University of Rome, 00184 Rome, Italy

a2 Linné FLOW Center, KTH Mechanics, SE-100 44 Stockholm, Sweden

Abstract

We study the two main phenomenologies associated with the transport of inertial particles in turbulent flows, turbophoresis and small-scale clustering. Turbophoresis describes the turbulence-induced wall accumulation of particles dispersed in wall turbulence, while small-scale clustering is a form of local segregation that affects the particle distribution in the presence of fine-scale turbulence. Despite the fact that the two aspects are usually addressed separately, this paper shows that they occur simultaneously in wall-bounded flows, where they represent different aspects of the same process. We study these phenomena by post-processing data from a direct numerical simulation of turbulent channel flow with different populations of inertial particles. It is shown that artificial domain truncation can easily alter the mean particle concentration profile, unless the domain is large enough to exclude possible correlation of the turbulence and the near-wall particle aggregates. The data show a strong link between accumulation level and clustering intensity in the near-wall region. At statistical steady state, most accumulating particles aggregate in strongly directional and almost filamentary structures, as found by considering suitable two-point observables able to extract clustering intensity and anisotropy. The analysis provides quantitative indications of the wall-segregation process as a function of the particle inertia. It is shown that, although the most wall-accumulating particles are too heavy to segregate in homogeneous turbulence, they exhibit the most intense local small-scale clustering near the wall as measured by the singularity exponent of the particle pair correlation function.

(Received April 15 2011)

(Reviewed December 30 2011)

(Accepted January 28 2012)

(Online publication April 05 2012)

Key Words:

  • particle/fluid flow;
  • turbulence simulation;
  • turbulent mixing

Correspondence:

c1 Email address for correspondence: carlomassimo.casciola@uniroma1.it

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