The impact of operating temperatures on the fluctuating flow field and precessing vortex core in cyclone separator using large-eddy simulations

The present study evaluates numerically the impact of the operating temperature of gas on the cyclone performance viz. the pressure drop, collection efficiency, and flow field details at an inlet velocity, Uin=15 m/s. The gas temperature in a range of 273–1073 K is considered to significantly vary the fluid density and viscosity. For an in-depth analysis, we use advanced closure large-eddy simulation (LES) with the standard Smagorinsky model for treating the unresolved scales. LES can accurately provide additional details on the precessing vortex core phenomena that give rise to enhanced fluctuations in the core region of the cyclone. Apart from the traditional fast Fourier transformation analysis to evaluate the periodicity in the signal, we also perform continuous wavelet transformation and empirical mode decomposition operation on the temporal velocity signals for a better understanding of the flow instabilities—the signals reveal variations of frequency components with time, indicating a non-stationary behavior. It has been observed that an increase in the gas temperature causes lateral contraction of the inner vortex followed by the reduction in its precessional frequency about the cyclone axis with a significantly increased level of noise in the spectra. Furthermore, both pressure losses and collection efficiency largely reduce due to the weakening of swirling strength and enhancement in the fluctuating velocity components with an increase in the gas temperature.