In this work, the inertial focusing of a microparticle in spiral channels is investigated numerically using a numerical solver developed in the framework of OpenFOAM open-source software. A special periodic boundary condition was implemented for a developed immersed boundary method to mimic the long microchannel, along with an adaptive meshing procedure to significantly reduce memory resources and shorten computation time. Simulation of a microparticle moving inside a square duct confirmed the existence of eight equilibrium positions over the channel’s cross section, four of which are located close to the channel wall centers, whereas the others are positioned near the corners, which has been reported in many studies before. Most importantly, we present, for the first time, a direct numerical simulation for the inertial sorting phenomenon of a microparticle in the spiral channel of rectangular and trapezoidal cross sections. Comprehensive analysis of the resulting lateral force field maps and Dean vortex configurations provides more insight into the focusing mechanism of a microparticle, which is beneficial for the design and optimization of cell separation microfluidic devices.
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