Numerical and theoretical investigations of the cavitation performance and instability for the cryogenic inducer

Cryogenic pumps are widely used in the fields of liquid rocket engines, liquefied natural gas (LNG) transportation, and International Thermonuclear Experimental Reactor (ITER) systems. An inducer is usually installed in front of the cryogenic pump to prevent the pump performance deterioration and flow instabilities caused by cavitation. The objectives of this paper are to investigate the influence of flow conditions on the thermal cavitation in a cryogenic inducer and purpose the theoretical models to predict the inducer performance and flow instabilities. In the present study, inducer working at different inlet temperature and rotating speed with liquid nitrogen was numerically investigated. The results show that the temperature drop around cavity regions increases and the cavity volume decreases with the increasing temperature, which leads to the delay of the drop of head coefficient. The increase of rotating speed leads to the increase of cavity volume and earlier deterioration of cavitation performance. The sub-synchronous rotating cavitation is observed in the inducer. It is characterized by the FFT analysis of cavity area fluctuation. The increase of temperature suppresses both the size and unevenness of the cavitation on each blade. Further analysis indicates that the temperature drop resulting from the cooling effect of evaporation around the cavitation area is significant due to the smaller liquid-vapor density ratio. A theoretical prediction model and a one-dimensional analysis model were developed to investigate the cavitation performance and instability. The theoretical models can accurately predict the influence of thermodynamic effect on the inducer cavitation and the pressure fluctuation inside the blade channel. These theoretical models can be applied to the design and testing of cryogenic pumps in practical applications.