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

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.

Regimes of heat transfer in particle suspensions

“…As concerns wall-bounded particulate flows, Lashgari et al (2014Lashgari et al ( , 2016 documented the existence of three different regimes when changing the volume fraction φ of neutrally-buoyant spherical particles and the flow Reynolds number Re (based on the flow bulk velocity): a laminar-like regime at low Re and low to intermediate values of φ, where the viscous stress dominates dissipation, a turbulent-like regime at high Reynolds number and low to intermediate φ where the turbulent Reynolds stress plays the main role in the momentum transfer across the channel and a third regime at higher φ, denoted as inertial shearthickening, characterised by a significant enhancement of the wall shear stress due to the particle-induced stresses. Indeed, thanks to novel and efficient numerical algorithms, many studies have been dedicated in the recent years to the turbulence modulation in the presence of solid particles (Lucci et al, 2010;Tanaka and Teramoto, 2015;Yu et al, 2016;Wang et al, 2016;Gupta et al, 2018;Costa et al, 2020). A decrease of the critical Reynolds number for transition to turbulence is reported by Matas et al (2003); Loisel et al (2013); Yu et al (2013); Lashgari et al (2015) for semi-dilute suspensions of neutrally-buoyant spherical particles, consistent with an enhancement of the turbulence activity documented at low volume fraction (up to 10%) in turbulent flows (Picano et al, 2015;Costa et al, 2016).…”

A lattice Boltzmann study of particle settling in a fluctuating multicomponent fluid under confinement

“…The motion of the particle is determined by Newton’s equation [ 37 ], and the evolution of the finite-size particle is solved with the leap-frog algorithm [ 46 ]. The integration of the leap-frog algorithm has been validated in previous studies for the finite-size particles in turbulent channel flows [ 47 , 48 ]. The bounce back boundary condition is implemented at the interface between the particle and the fluid [ 36 ].…”

Macroemulsion-mediated synthesis of fibrous ZnO microrods and their surface morphology contribution to the high photocatalytic degradation rate

“…Currently, there are many reports about the preparation of ZnO nano-/microrods for various applications, including photocatalysts. 20,21 As a photocatalyst in an aqueous system, the rod shape of ZnO has many advantages, such as being more vigorous while stirring 22 and a higher surface-to-volume ratio. 23 ZnO nano-/microrods with higher aspect ratios have a higher surface area, which facilitates higher adsorption of target molecules, leading to higher photocatalytic activity.…”