Influence of thermodynamic effect on sub-synchronous rotating cavitation and surge mode oscillation

To investigate the influence of the thermodynamic effect on the sub-synchronous rotating cavitation, we conducted experiments in which liquid nitrogen was set at different temperatures (74 K, 78 K and 83 K) with focusing on the fluctuation of the cavity length. Sub-synchronous rotating cavitation appeared at lower cavitation numbers in liquid nitrogen at 74 K, which was the same as that in cold water. In contrast, in liquid nitrogen at 83 K, the occurrence of sub-synchronous rotating cavitation was suppressed on the increase of thermodynamic effect due to the rising temperature. Furthermore, the unevenness of cavity length under the synchronous rotating cavitation was also decreased by the thermodynamic effect. However, surge mode oscillation occurred simultaneously under the condition of weakened synchronous rotating cavitation. Cavity lengths on the blades oscillated with the same phase maintained the uneven cavity pattern. It was estimated that the thermodynamic effect weakened the peripheral cavitation instability, i.e., synchronous rotating cavitation, but axial cavitation instability, i.e., surge mode oscillation, was induced easily because of the synchronization of the cavity fluctuation with an acoustic resonance in the present inlet-pipe system.