Fully-resolved prolate spheroids in turbulent channel flows: A lattice Boltzmann study

Eshghinejadfard, Amir; Hosseini, Seyed Ali; Thévenin, Dominique

doi:10.1063/1.5002528

Cited by 42 publications

(28 citation statements)

References 48 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Wang (2017) studied spheroidal particles in a turbulent plane Couette flow with aspect ratios ranging form 0.5 to 2 at 5% volume fraction, revealing that the particle distribution of spheroids in the flow is not significantly modified by their shapes. Eshghinejadfard et al (2017) performed simulations of prolate particles up to 1.5% volume fraction in a turbulent channel flow, showing the disappearance of the particle wall-layer, previously observed for spheres (Picano et al 2015) and also slight turbulence attenuation with respect to the single-phase flow. Finite-size rigid fibers are studied in the work of (Do-Quang et al 2014) at low volume fractions around 0.1%.…”

Section: Introductionmentioning

confidence: 69%

Turbulence modulation in channel flow of finite-size spheroidal particles

Ardekani

Brandt

2018

J. Fluid Mech.

View full text Add to dashboard Cite

Finite-size particles modulate wall-bounded turbulence, leading for the case of spherical particles to increased drag also owing to the formation of a particle wall layer. Here, we study the effect of particle shape on the turbulence in suspensions of spheroidal particles at volume fraction φ = 10% and show how the near-wall particle dynamics deeply changes with the particle aspect ratio and how this affects the global suspension behavior. Direct numerical simulations are performed using a direct-forcing immersed boundary method to account for the dispersed phase, combined with a soft-sphere collision model and lubrication corrections for short-range particle-particle and particle-wall interactions. The turbulence reduces with the aspect ratio of oblate particles, leading to drag reduction with respect to the single phase flow for particles with aspect ratio AR 1/3, when the significant reduction in Reynolds shear stress is more than the compensation by the additional stresses, induced by the solid phase. Oblate particles are found to avoid the region close to the wall, travelling parallel to it with small angular velocities, while preferentially sampling high-speed fluid in the wall region. Prolate particles, also tend to orient parallel to the wall and avoid its vicinity. Their reluctancy to rotate around spanwise axis reduce the wall-normal velocity fluctuation of the flow and therefore the turbulence Reynolds stress similar to oblates; however, they undergo rotations in wallparallel planes which increases the additional solid stresses due to their relatively larger angular velocities compared to the oblates. These larger additional stresses compensates for the reduction in turbulence activity and leads to a wall-drag similar to that of singlephase flows. Spheres on the other hand, form a layer close to the wall with large angular velocities in spanwise direction, which increases the turbulence activity in addition to exerting the largest solid stresses on the suspension, in comparison to the other studied shapes. Spherical particles therefore increase the wall-drag with respect to the singlephase flow.

show abstract

Section: Introductionmentioning

confidence: 69%

Turbulence modulation in channel flow of finite-size spheroidal particles

Ardekani

Brandt

2018

J. Fluid Mech.

View full text Add to dashboard Cite

show abstract

“…The previously mentioned challenges and limitations of experimental and theoretical approaches makes the use of advanced numerical tools a necessity for obtaining detailed information; despite the well-known limitations in terms of Reynolds numbers that can be reached in simulations (Prosperetti 2015). Lately, several groups have been successfully using numerical algorithms for interface-resolved direct numerical simulations (DNS) of different turbulent flows laden with finite size particles: examples are suspensions in isotropic turbulence (Ten Cate et al 2004;Lucci et al 2010), vertical channel flow (Uhlmann 2008), sedimentation (Chouippe & Uhlmann 2015;Fornari et al 2016b), bed load transport (Kidanemariam & Uhlmann 2014;Vowinckel et al 2014), channel transport of mono-dispersed particles (Wang et al 2016;Yu et al 2016;Wang et al 2017), and recently of poly-disperse (Lashgari et al 2017;Fornari et al 2018) and non-spherical particles (Ardekani et al 2017;Eshghinejadfard et al 2017). Likewise, the present work uses such simulations to study turbulent channel transport of neutrally-buoyant finite size spheres.…”

mentioning

confidence: 99%

Effects of the finite particle size in turbulent wall-bounded flows of dense suspensions

et al. 2018

View full text Add to dashboard Cite

We use interface-resolved numerical simulations to study finite-size effects in turbulent channel flow of neutrally-buoyant spheres. Two cases with particle sizes differing by a factor of 2, at the same solid volume fraction of 20% and bulk Reynolds number are considered. These are complemented with two reference single-phase flows: the unladen case, and the flow of a Newtonian fluid with the effective suspension viscosity of the same mixture in the laminar regime. As recently highlighted in Costa et al. (2016), a particle-wall layer is responsible for deviations of the mesoscale-averaged statistics from what is observed in the continuum limit where the suspension is modeled as a Newtonian fluid with (higher) effective viscosity. Here we investigate in detail the fluid and particle dynamics inside this layer and in the bulk. In the particle-wall layer, the near wall inhomogeneity has an influence on the suspension micro-structure over a distance proportional to the particle size. In this layer, particles have a significant (apparent) slip velocity that is reflected in the distribution of wall shear stresses. This is characterized by extreme events (both much higher and much lower than the mean). Based on these observations we provide a scaling for the particle-to-fluid apparent slip velocity as a function of the flow parameters. We also extend the scaling laws in Costa et al. (2016) to second-order Eulerian statistics in the homogeneous suspension region away from the wall. The results show that finite-size effects in the bulk of the channel become important for larger particles, while negligible for lower-order statistics and smaller particles. Finally, we study the particle dynamics along the wall-normal direction. Our results suggest that single-point dispersion is dominated by particle-turbulence (and not particle-particle) interactions, while differences in two-point dispersion and collisional dynamics are consistent with a picture of shear-driven interactions.

show abstract

“…Based on the thickness of the particle wall-layer, they proposed a relation able to predict the friction Reynolds number as function of the bulk Reynolds number. Indeed, the particle wall-layer was found to have a significant effect on the modulation of the near-wall turbulence, as in the case of non-spherical particles (Ardekani et al 2017;Eshghinejadfard et al 2017; where the absence of this layer leads to attenuation of the turbulence activity, resulting in drag reduction. Picano et al (2015) attribute the formation of the near-wall layer of spherical particles to the strong wall-particle lubrication interaction that stabilizes the particle wall-normal position, forcing it to roll on the wall.…”

Section: Introductionmentioning

confidence: 99%

Turbulent flow of finite-size spherical particles in channels with viscous hyper-elastic walls

Ardekani¹,

Rosti²,

Brandt³

2019

J. Fluid Mech.

View full text Add to dashboard Cite

We study single-phase and particulate turbulent channel flows, bounded by two incompressible hyper-elastic walls at bulk Reynolds number 5600. Different wall elasticities are considered with and without a 10% volume fraction of finite-size neutrally-buoyant rigid spherical particles. A fully Eulerian formulation is employed to account for the fluid-structure interaction at the elastic walls interfaces together with a direct-forcing immersed boundary method (IBM) to model the coupling between the fluid and the particles. The elastic walls are assumed to be made of a neo-Hookean material. We report a significant drag increase and an enhancement of the turbulence activity with growing wall elasticity for both single-phase and particulate cases in comparison with the single phase flow over rigid walls. A drag reduction and a turbulence attenuation is obtained for the particulate cases with highly elastic walls, albeit with respect to the single-phase flow of the same wall elasticity; whereas, an opposite effect of the particles is observed on the flow of the less elastic walls. This is explained by investigating the nearwall turbulence of highly elastic walls, where the strong asymmetry in the magnitude of wall-normal velocity fluctuations (favouring the positive v ), is found to push the particles towards the channel centre. The particle layer close to the wall is shown to contribute to the turbulence production by increasing the wall-normal velocity fluctuations, while in the absence of this layer, smaller wall deformation and in turn a turbulence attenuation is observed. We further address the effect of the volume fraction at a moderate wall elasticity, by increasing the particle volume fraction up to 20%. Migration of the particles from the interface region is found to be the cause of a further turbulence attenuation, in comparison to the same volume fraction in the case of rigid walls. However, the particle induced stress compensates for the loss of the Reynolds shear stress, thus, resulting in a higher overall drag for the case with elastic walls. The effect of wall-elasticity on the drag is reported to reduce significantly with increasing volume fraction of particles.

show abstract

Fully-resolved prolate spheroids in turbulent channel flows: A lattice Boltzmann study

Cited by 42 publications

References 48 publications

Turbulence modulation in channel flow of finite-size spheroidal particles

Turbulence modulation in channel flow of finite-size spheroidal particles

Effects of the finite particle size in turbulent wall-bounded flows of dense suspensions

Turbulent flow of finite-size spherical particles in channels with viscous hyper-elastic walls

Contact Info

Product

Resources

About