In this article, computational fluid dynamics (CFD) is used to compute the unsteady, compressible flow caused by a flat falling circular disk. CFD results are coupled with a particle trajectory model to determine particle trajectories for different particle sizes and examine which particles are trapped or ejected from the closing gap. CFD results show that the normalized radial velocity profiles are self similar for different Reynolds numbers based on the gap height, and that flow compressibility results in a density increase toward the center of the disk for decreasing gap height. To efficiently couple CFD results with the particle trajectory model, a regression model representing both the velocity field and density variation inside the gap is developed and coupled with a particle detachment model. Particle trajectories are shown to be sensitive to the flow compressibility and must be taken into account. The escaped and trapped particle distribution is computed for a thin mono-layer of Arizona Test Dust under the disk. The simulations show that higher impact velocities tend to cause more of the heavier and larger particles to be trapped under the disk because they are catapulted from the floor and are quickly driven down again by the descending disk.