Flow visualization of non-contacting mechanical seals with bidirectional rotation

Abstract

Abstract Non-contacting mechanical seals are used as a shaft seal in a turbomachinery. A few micrometers thin lubrication film is formed by grooves on the seals. Various groove shapes were presented, and most of these grooves were designed for unidirectional rotation. However, reverse rotation occurs accidentally in the turbomachinery. In this study, the performance of two type unidirectional grooves was investigated by measuring the pressure in a chamber which means sealed fluid pressure and visualizing the flow in the lubrication film with bidirectional rotation. The measurement results of pressure under forward rotation showed that the pressures fluctuated as rotational speeds increased by hydrodynamic pressure. By contrast, under reverse rotation, the amount of fluctuation was smaller and almost not changed with increasing rotational speeds. In addition, the flow visualization results showed the increase of pressure drop areas and occurrence of gas phase. This indicates the decrease in load capacity and film stiffness. In contrast, the discharging flow from inner to outer side or the breakage of the film were confirmed and prevented fluid leaking. In summary, the results showed the degradation of lubrication characteristics though the no degradation of a sealing performance.