### 2019

Kim Alards; Rudie Kunnen; Herman Clercx; Federico Toschi

Statistical properties of thermally expandable particles in soft-turbulence Rayleigh-Bénard convection Journal Article

In: European Physical Journal E : Soft Matter, vol. 42, no. 9, 2019, ISSN: 1292-8941.

Abstract | Links | BibTeX | Tags: Problems and Applications, Topical issue: Flowing Matter

@article{4008646d8f584ce7a26171d228d6b022,

title = {Statistical properties of thermally expandable particles in soft-turbulence Rayleigh-Bénard convection},

author = {Kim Alards and Rudie Kunnen and Herman Clercx and Federico Toschi},

doi = {10.1140/epje/i2019-11882-y},

issn = {1292-8941},

year = {2019},

date = {2019-01-01},

journal = {European Physical Journal E : Soft Matter},

volume = {42},

number = {9},

publisher = {Springer},

abstract = {Abstract.: The dynamics of inertial particles in Rayleigh-Bénard convection, where both particles and fluid exhibit thermal expansion, is studied using direct numerical simulations (DNS) in the soft-turbulence regime. We consider the effect of particles with a thermal expansion coefficient larger than that of the fluid, causing particles to become lighter than the fluid near the hot bottom plate and heavier than the fluid near the cold top plate. Because of the opposite directions of the net Archimedes’ force on particles and fluid, particles deposited at the plate now experience a relative force towards the bulk. The characteristic time for this motion towards the bulk to happen, quantified as the time particles spend inside the thermal boundary layers (BLs) at the plates, is shown to depend on the thermal response time, τ T, and the thermal expansion coefficient of particles relative to that of the flui},

keywords = {Problems and Applications, Topical issue: Flowing Matter},

pubstate = {published},

tppubtype = {article}

}

Abstract.: The dynamics of inertial particles in Rayleigh-Bénard convection, where both particles and fluid exhibit thermal expansion, is studied using direct numerical simulations (DNS) in the soft-turbulence regime. We consider the effect of particles with a thermal expansion coefficient larger than that of the fluid, causing particles to become lighter than the fluid near the hot bottom plate and heavier than the fluid near the cold top plate. Because of the opposite directions of the net Archimedes’ force on particles and fluid, particles deposited at the plate now experience a relative force towards the bulk. The characteristic time for this motion towards the bulk to happen, quantified as the time particles spend inside the thermal boundary layers (BLs) at the plates, is shown to depend on the thermal response time, τ T, and the thermal expansion coefficient of particles relative to that of the flui

### 2018

A Gupta; H J H Clercx; F Toschi

Effect of particle shape on fluid statistics and particle dynamics in turbulent pipe flow Journal Article

In: European Physical Journal E : Soft Matter, vol. 41, no. 10, 2018, ISSN: 1292-8941.

Abstract | Links | BibTeX | Tags: Problems and Applications, Topical issue: Flowing Matter

@article{e5b00c30eb0a4b9296c91a4696acba91,

title = {Effect of particle shape on fluid statistics and particle dynamics in turbulent pipe flow},

author = {A Gupta and {H J H } Clercx and F Toschi},

doi = {10.1140/epje/i2018-11724-6},

issn = {1292-8941},

year = {2018},

date = {2018-01-01},

journal = {European Physical Journal E : Soft Matter},

volume = {41},

number = {10},

publisher = {Springer},

abstract = {Anisotropic particles are present in many natural and industrial flows. Here we perform direct numerical simulation (DNS) of turbulent pipe flows with dispersed finite-size prolate spheroids simulated by means of the lattice Boltzmann method (LBM). We consider three different particle shapes: spheroidal (aspect ratio 2 and 3) and spherical. These three simulations are complemented with a reference simulation of a single-phase flow. For the sake of comparison, all simulations, laden or unladen have the same energy input. The flow geometry used is a straight pipe with length eight times its radius where the fluid is randomly seeded with 256 finite-size particles. The volume fraction of particles in the flow has been kept fixed at 0.48% by varying the major and minor axis of each particle such that their volume remains the same. We studied the effect of different particle shapes on particle dynamics and orientation, as well as on the flow modulation. We show that the local accumulation of spheres close to the wall decreases for spheroids with increasing aspect ratio. These spheroidal particles rotate slower than spheres near to the wall and tend to stay with their major axes aligned to the flow streamwise direction. Despite the lower rotation rates, a higher intermittency in the rotational rates was observed for spheroids and this increase at increasing the aspect ratio. The drag reduction observed for particles with higher aspect ratio have also been investigated using the one-dimensional energy and dissipation spectra. These results point to the relevance of particle shapes on their dynamics and their influence on the turbulent flow.},

keywords = {Problems and Applications, Topical issue: Flowing Matter},

pubstate = {published},

tppubtype = {article}

}

Anisotropic particles are present in many natural and industrial flows. Here we perform direct numerical simulation (DNS) of turbulent pipe flows with dispersed finite-size prolate spheroids simulated by means of the lattice Boltzmann method (LBM). We consider three different particle shapes: spheroidal (aspect ratio 2 and 3) and spherical. These three simulations are complemented with a reference simulation of a single-phase flow. For the sake of comparison, all simulations, laden or unladen have the same energy input. The flow geometry used is a straight pipe with length eight times its radius where the fluid is randomly seeded with 256 finite-size particles. The volume fraction of particles in the flow has been kept fixed at 0.48% by varying the major and minor axis of each particle such that their volume remains the same. We studied the effect of different particle shapes on particle dynamics and orientation, as well as on the flow modulation. We show that the local accumulation of spheres close to the wall decreases for spheroids with increasing aspect ratio. These spheroidal particles rotate slower than spheres near to the wall and tend to stay with their major axes aligned to the flow streamwise direction. Despite the lower rotation rates, a higher intermittency in the rotational rates was observed for spheroids and this increase at increasing the aspect ratio. The drag reduction observed for particles with higher aspect ratio have also been investigated using the one-dimensional energy and dissipation spectra. These results point to the relevance of particle shapes on their dynamics and their influence on the turbulent flow.