Abstract: Numerical simulation of air core formation inside hydrocyclones was carried out by using a commercial computational fluid dynamics(CFD)modeling software package ANSYS/Fluent based on the Reynolds stress model(RSM)for the turbulence calculation and volume of fluid(VOF)model for capturing the airliquid interface. The numerical simulation shown that the air core formed when the time was 07s，which was in good agreement with the physical experiment conducted at a similar condition. The air of the air core entered the hydrocyclone from the underflow outlet and exhausted from the overflow outlet. The largest swing of the air core occurred in the region close to the underflow area，and a protuberance resembling the Adam′s apple appeared when the air core entered the overflow pipe. Unnecessary energy was consumed， but no extra perturbation was brought into the flow field by air core. Under current design and operation conditions， the structural parameters such as overflow and underflow outlet diameter and cone angle have more significant effects on the air core diameter than the operational parameter like the feeding rate.

Key words: hydrocyclone, air core, numerical simulation, PIV flow field measurements, influencing factor