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Fluid flow laden with a single finite size neutrally buoyant particle over a confined microcavity adjacent to a main straight microchannel is numerically simulated by a fully resolved simulation method. This method is based on coupled immersed boundary–lattice Boltzmann method, which can directly resolve the fluid flow and the interactions between fluid and particles without any empirical models. The evolution of the fluid microvortex and the motions of the particle, such as trapping, orbiting, and rotating, in a confined microcavity are investigated as a function of Reynolds number ranging from 5 to 250. The results reveal that the topology structure of the microvortex changes from local apex ear, to globally crescentic and then triangle as Reynolds number increases. Three phases for particle stable and unstable entrapping behavior and four particle-trapping modes are observed and identified. The particle-trapping pathway varies from outer to inner, invariable, inner to outer, and inner to escape corresponding to different Reynolds numbers. The mechanisms for this phenomenon are revealed by a new improved competing model between outward centrifugal force and inward inertial lift force. Finally, the orbiting and rotating motion of the particle is quantitatively analyzed for the first time.
Particle orbiting and rotating behavior in the microcavity and the distribution of pressure coefficient on the particle surface at different particle positions.