Abstract
Inertial point particles suspended in a two-dimensional unsteady circular cylinder flow at Re=100 are studied by one-way coupled three-dimensional numerical simulations. The striking clustering pattern in the near-wake is strongly correlated with the periodically shed Kármán vortex cells. The particles are expelled from the vortex cores due to the centrifugal mechanism and coherent voids encompassing the local Kármán cells are therefore observed. The particle clustering at the upstream side of each void hole form a smooth edge, where the particle velocity magnitude is consistently lower than at the downstream edge of the voids. The trajectories of these particles originate from the side of the cylinder where the sign of vorticity is opposite to that of the vortex encompassed by the corresponding void hole. The particles are seen to decelerate along a substantial part of their trajectories. Particle inertia is parameterized by means of a Stokes number Sk and smooth edges around the void holes still exist when Sk is increased, although their formation is delayed due to larger inertia. Increasing inertia contributes to a decoupling of the particle acceleration from the slip velocity, which almost coincided at Sk=1.
Highlights
Particle-laden flows around natural obstacles and man-made bluff bodies are frequently encountered in nature and industry
The unsteady 2D flow is laden with inertial spherical particles characterized by a dimensionless Stokes number (Sk)
Previous studies dealt with particle dispersion in cylinder wake flow and/or vortex streets from various aspects, the topology of the particle concentration has never been analyzed in detail, to how we have done in the present manuscript
Summary
Particle-laden flows around natural obstacles and man-made bluff bodies are frequently encountered in nature and industry. Even though the entering flow is regular and smooth, the fluid motion in the wake of the obstacle becomes more complex and comprises a variety of characteristic length and time scales. Insight in particle transportation and dispersion mechanisms in common bluff-body wakes may promote mitigation of industrial pollution and a better understanding of natural phenomena, such as scouring around offshore wind turbine foundations and clogging of steam generators in nuclear power plants at large scales, as well as enhancing the mixing performance of microfluidic reactors at small scales. Microfluidic systems are commonly applied in the lab-on-a-chip biological devices, wherein the flows are almost always laminar defined by a tiny pore scale. The mixing or demixing processes can be manipulated with the funda-
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