The present work investigates various swirl flow motions for the cavitation characteristics through numerical simulation of the four-phase cavitating flow in a Venturi tube. A three-dimensional Eulerian–Eulerian approach available in a commercial CFD software was used in conjunction with the k−ω SST scheme and Schnerr–Sauer cavitation model adopted for solid–liquid–vapor–air flows. The results of simulations are validated against the experimental data obtained in our previous study (Shi et al., 2020). Excellent predictions of flow characteristics were obtained by various solid concentrations. The results reveal that the intense swirl motions can substantially affect the movement of cavitation bubbles and micro particles. When intensive swirl motion is imposed in the process, an efficient separation of micro particles are of significant importance A higher swirl strength is of benefit to cavitation performance and degree of protection on the inner surface of throat walls from the cavitation erosion but not solid erosion. In addition, the turbulent viscosity analysis predicts weaker turbulent viscosity ratio, resulting in higher multi-factor coupling cavitation production in the divergent region. The primary and secondary swirling re-entrant jets are identified and analyzed as well. This work illustrates main features of the swirl impact on the cavitation phenomena in four-phase flows: solid–liquid–vapor–air flows. This information can strongly support the design, optimization, and application of hydrodynamic cavitation devices in the field of separation process in industrial wastewater or sludge processing. •The impact of swirls on the separation phenomena in four-phase flows.•The intense swirl motions substantially affect the separation of micro particles.•A higher swirl strength is of benefit to separation/cavitation performances.