2014/06/06 by Markus Uhlmann, Todor Doychev
Earth and Planetary Sciences · Engineering · Mathematics · Physics and Astronomy · #Aeolian processes and effects #Classical mechanics #Cluster (spacecraft) #Cluster analysis #Geology #Granular flow and fluidized beds #Magnetosphere particle motion #Mathematics #Mechanics #Motion (physics) #Particle (ecology) #Particle Dynamics in Fluid Flows #Physics #Quantum mechanics #SPHERES #Sediment #Sedimentation #Settling #Statistics #Suspension (topology) #Terminal velocity #Thermodynamics #physics.flu-dyn
paper · pdf · doi:10.1017/jfm.2014.330
published as J. Fluid Mech., 752:310-348, 2014 · accepted for publication in J. Fluid Mech. (2014), more data at this http URL http://www.ifh.kit.edu/dns_data
arxiv created 2014/06/06 · openalex publication_date 2014/07/04 · arxiv updated 2014/09/02 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Abstract Direct numerical simulation of the gravity-induced settling of finite-size particles in triply periodic domains has been performed under dilute conditions. For a single solid-to-fluid-density ratio of 1.5 we have considered two values of the Galileo number corresponding to steady vertical motion ( \def \xmlpi #1\def \mathsfbi #1\boldsymbol \mathsf #1\let ≤ =\leqslant \let ≤ =\leqslant \let ≥ =\geqslant \let ≥ =\geqslant \def Pr \mathit Pr\def \Fr \mathit Fr\def \Rey \mathit ReGa=121 ) and to steady oblique motion ( Ga=178 ) in the case of one isolated sphere. For the multiparticle system we observe strong particle clustering only in the latter case. The geometry and time scales related to clustering are determined from Voronoï tessellation and particle-conditioned averaging. As a consequence of clustering, the average particle settling velocity is increased by 12 % as compared with the value of an isolated sphere; such a collective effect is not observed in the non-clustering case. By defining a local (instantaneous) fluid velocity average in the vicinity of the finite-size particles it is shown that the observed enhancement of the settling velocity is due to the fact that the downward fluid motion (with respect to the global average) which is induced in the cluster regions is preferentially sampled by the particles. It is further observed that the variance of the particle velocity is strongly enhanced in the clustering case. With the aid of a decomposition of the particle velocity it is shown that this increase is due to enhanced fluid velocity fluctuations (due to clustering) in the vicinity of the particles. Finally, we discuss a possible explanation for the observation of a critical Galileo number marking the onset of clustering under dilute conditions.