Multiscale preferential sweeping of particles settling in turbulence

Tom, Josin; Bragg, Andrew D.

doi:10.1017/jfm.2019.337

Cited by 53 publications

(94 citation statements)

References 53 publications

(129 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, for F r = 0.052, there is a local concentration at which the mean settling velocity is maximum, and then decreases for higher concentrations. If we assume that larger Voronoï volumes are associated with larger flow scales, then this is consistent with the arguments in [35] that as F r is decreased, the scales of the flow responsible for enhancing the particle settling velocity increase. The results also show that increasing R λ can significantly increase the settling velocities, especially for St ≥ 0.5.…”

Section: B Particle Settling Velocitiessupporting

confidence: 85%

“…The results also show that increasing R λ can significantly increase the settling velocities, especially for St ≥ 0.5. This is explained by the recent theoretical analysis of [35] that shows that as R λ is increased, more and more energetic flow scales are introduced to the flow that are able to contribute to the particle settling velocity enhancement through the preferential sweeping mechanism described below.…”

Section: B Particle Settling Velocitiesmentioning

confidence: 99%

“…Our results also show that this difference increases with increasing R λ , with a nonmonotonic dependence on F r (since the results are zero for F r = ∞). The average settling velocity of all particles is known to increase with increasing R λ , which is principally due to the enhanced range of scales for the particles to interact with as R λ grows [35]. However, the R λ dependence of the results in figure 16 would seem to be due to something more subtle to this, since all particles in the flow, whether clustered or not, would be subject to the enhanced range of scales available for the particles to interact with as R λ grows.…”

Section: Fig 13: Standard Deviation Of Voronoï Cells Of Clusters As mentioning

confidence: 99%

“…Again, however, the effects of R λ and F r on the results was not systematically explored. It has also been recently shown theoretically and numerically how the settling of particles in turbulence is affected by a range of flow scales that depends on St, R λ , and F r [35]. It is therefore of interest to explore the effect of St, R λ , and F r on the particle settle speeds using Voronoï analysis in order to gain further insights into the multiscale nature of the problem.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Local analysis of the clustering, velocities, and accelerations of particles settling in turbulence

Momenifar

Bragg

2020

Phys. Rev. Fluids

Self Cite

View full text Add to dashboard Cite

Using 3D Voronoï analysis, we explore the local dynamics of small, settling, inertial particles in isotropic turbulence using Direct Numerical Simulations (DNS). We independently vary the Taylor Reynolds number R λ ∈ [90, 398], Froude number F r ≡ a η /g ∈ [0.052, ∞] (where a η is the Kolmogorov acceleration, and g is the acceleration due to gravity), and Kolmogorov scale Stokes number St ≡ τ p /τ η ∈ [0, 3]. In agreement with previous results using global measures of particle clustering, such as the Radial Distribution Function (RDF), we find that for small Voronoï volumes (corresponding to the most clustered particles), the behavior is strongly dependent upon St and F r, but only weakly dependent upon R λ , unless St > 1. However, larger Voronoï volumes (void regions) exhibit a much stronger dependence on R λ , even when St ≤ 1, and we show that this, rather than the behavior at small volumes, is the cause of the sensitivity of the standard deviation of the Voronoï volumes that has been previously reported. We also show that the largest contribution to the particle settling velocities is associated with increasingly larger Voronoï volumes as the settling parameter Sv ≡ St/F r is increased.Our local analysis of the acceleration statistics of settling inertial particles shows that clustered particles experience a net acceleration in the direction of gravity, while particles in void regions experience the opposite. The particle acceleration variance, however, is a convex function of the Voronoï volumes, with or without gravity, which seems to indicate a non-trivial relationship between the Voronoï volumes and the sizes of the turbulent flow scales. Results for the variance of the fluid acceleration at the inertial particle positions are of the order of the square of the Kolmogorov acceleration and depend only weakly on Voronoï volumes. These results call into question the "sweep-stick" mechanism for particle clustering in turbulence which would lead one to expect that clustered particles reside in the special regions where the fluid acceleration is zero (or at least small).We then consider the properties of particles in clusters, which are regions of connected Voronoï cells whose volume is less than a certain threshold. The results show self-similarity of the clusters, and that the statistics of the cluster volumes depends only weakly on St, with a stronger dependance on F r and R λ . Finally, we compare the average settling velocities of all particles in the flow with those in clusters, and show that those in the clusters settle much faster, in agreement with previous work. However, we also find that this difference grows significantly with increasing R λ and exhibits a non-monotonic dependence on F r. The kinetic energy of the particles, however, are almost the

show abstract

Section: B Particle Settling Velocitiessupporting

confidence: 85%

Section: B Particle Settling Velocitiesmentioning

confidence: 99%

Section: Fig 13: Standard Deviation Of Voronoï Cells Of Clusters As mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations