Analysis on the patterns of precessing frequency characteristics and energy separation processes in a Ranque-Hilsch vortex tube

Recently, the particular energy separation of the vortex tube was thought to be caused by the energy transferred from the inner core stream to the outer periphery stream through the precessing vortex core, and the precessing frequency is a remarkable signal released by the vortex core. To study the basic distribution of the precessing frequency and the relationship between the frequency and energy separation, precessing frequency characteristics were analysed in a vortex tube with a diameter of 30 mm in this paper. To achieve this, axial velocity time series were obtained by LDV measurements. It is demonstrated that the impact of the precessing vortex core on the flow field is consistent under different radial positions at the same axial position. However, the impact gradually weakens downstream. In addition, the precessing characteristics vanish within the swirl decay zone, which results in the deterioration of the energy separation performance. An enhancement in the inlet pressure results in an improvement in the performance and a significant increase in the magnitude of the peak frequency. In addition, the energy separation process and performance under increasing inlet pressure were analysed. It was observed that the growth of the precessing frequency imparts a higher energy transfer capability, which results in higher performance. The patterns of large-scale vortices and energy separation of the vortex tube were determined based on these observations. In addition, the enhancement in the precessing frequency may offer a novel concept based on which the performance of the vortex tube can be enhanced. Finally, a large eddy simulation was recommended to obtain more detailed information on large-scale precessing vortices.