Particles turbulence interactions in boundary layers

Abstract

Turbulent dispersed flows in boundary layers are crucial in a number of industrial and environmental applications. In most applications, the key information is space distribution of particles which is known to be strongly non-homogeneous. Specifically, inertial particles distribute preferentially avoiding strong vortical regions and segregating into straining regions. The vortical boundary layer structures control momentum, mass, heat, and particle transfer. Coherent structures bring particles toward the wall and away from the wall and favour particle segregation in the viscous region giving rise to nonuniform particle distribution profiles which peak close to the wall. The reason for this behavior is particle inertia, which filters the high frequency turbulence fluctuations. The object of this work is to review the current understanding of turbulent boundary layer dynamics and to examine the mechanisms for particle transfer, segregation, and preferential distribution. The physical mechanisms discussed and proposed are based on Direct Numerical Simulations of turbulence and Lagrangian tracking of inertial particles.

Anisotropy in pair dispersion of inertial particles in turbulent channel flow

“…This causes fluctuations of particle concentration that alter the structure of particle patterns. This phenomenology has been demonstrated and discussed in many experimental works, 2,20 as well as numerical studies [21][22][23][24][25][26][27][28] and theoretical analyses. 17,[29][30][31] From a modelling standpoint, reproducing accurately pair relative velocity and dispersion statistics is crucial to predict the effect of particle clustering on turbulent collisions and sedimentation.…”

“…Inclusion of additional forces such as gravity and lift 44,45 or incorporation of two-way coupling effects would just add quantitative corrections within the range of parameters examined-particle dimension (see Table I for details), density, and concentration-and would not modify the quality of the model. 24 …”

“…A possible explanation to this finding is related to the well-known phenomena of inertial particle segregation and preferential concentration. 2,21,24 It has been long established that heavy particles in low Reynolds turbulence are governed by fluid strain, namely centrifuged out of the turbulent eddies and accumulated in regions of low vorticity and high strain rate. In the near-wall region, the centrifuging phenomenology implies that particles are preferentially displaced in the cross-stream plane by the turbulent vortical structures which populate this region and generate areas of high streamwise vorticity alternated to areas of high cross-stream strain.…”

The influence of local meteorological conditions on the circadian rhythm of corn (Zea mays L.) pollen emission

“…In addition, it has been shown by direct numerical simulations (DNS, e.g. Soldati, 2005) that the ejection-sweep cycles are instrumental in the entrainment, dispersal and deposition of heavy particles. Ejection-sweep cycles in corn canopy flows have been investigated by Shaw et al (1983) and by Zhu et al (2006Zhu et al ( , 2007a using a technique called Quadrant-Hole (Q-H) analysis (Willmarth and Lu, 1972).…”

Turbulence modulation and drag reduction by spherical particles

“…The current understanding of the complex behavior of inertial spherical particles in turbulent wall flows was summarized in a keynote lecture by Soldati. 10 The survey of experimental studies and two-way coupled computer simulations by Balachandar and Eaton 11 furthermore addressed the turbulence modulation observed in the presence of inertial particles. In dilute suspensions where particle collisions are of negligible importance, the fluid turbulence may be affected by an enhanced dissipation due to the particles, kinetic energy transfer between the fluid and the particles, and wakes formed in the lee of the solid particles.…”