An Eulerian-Eulerian two-phase numerical model is employed to investigate the behavior of particles in oscillating gas flows with neglect of the effect of particles on gas flow field and the interphase heat and mass transfer. Meanwhile, a theoretical model for the analysis of particle clustering in oscillating gas flows is presented, in which the particles are tracked by the Lagrangian method and the particle concentration is calculated in the Euler frame. These two models complement each other with the aim to reveal the cause of formation and Characteristics of particle clustering in oscillating flows. The results show that the occurrence of particle trapping/dispersion can be essentially attributed to the relaxation of particle velocity from its initial value to the mean value. The corresponding particle concentration shift is primarily determined by the particle initial velocity and mean velocity, but independent of the particle diameter and the gas oscillation. Two types of particle clustering are identified based on the different causes. The first type can be attributed to the relaxation of particle velocity from its mean value to the instantaneous gas velocity. The particle concentration oscillates with the same frequency of gas oscillation and travels at the local mean particle velocity which is equal to that of the gas. The second type is due to the modulation of particle velocity by the acoustic wave introduced at the inlet by gas velocity oscillation. The particle concentration oscillates at the frequency of gas oscillation and travels at the sound speed of the gas. The corresponding amplitude is much smaller than the first type. The results can also be extended to multidimensional space. (C) 2017 Elsevier B.V. All rights reserved.