A Numerical Simulation Study of the Dynamic Instability of Gas Swirling Flows in Cyclones

Abstract

The gas–phase flow field within a cyclone plays a critical role in the particle separation process. While previous research has primarily focused on the steady–state, time–averaged characteristics of this flow field, there has been limited investigation into its dynamic instability. This study seeks to address this gap by examining the dynamic instability of gas swirling flows in cyclones, offering new insights into their spatial and temporal dimensions. Numerical simulations were performed via large eddy simulation (LES) for the gas swirling flow in a reverse cyclone and tangential velocity was measured with a hot–wire anemometer (HWA). The model’s accuracy was validated against experimental data. The results demonstrate that the distributions of instantaneous tangential velocity and pressure exhibit spatial asymmetry and temporal instability across different sections of the cyclone. The dynamic instability of the gas swirling flow in the cyclone is the superposition of the spatial asymmetry and the temporal instability. These instabilities are more pronounced in the internal regions than the outer regions. Dynamic instability arises from the combined effects of rotational dynamics and wall curvature, leading to an eccentric rotation of the swirling center, particularly evident in the lower sections of the cyclone cone. This instability increases fluctuations in the instantaneous parameters, enhancing turbulence intensity and fine particle diffusion, and ultimately impairing both separation efficiency and particle size efficiency.