Kengo Kikuta

Thermodynamic Effect on a Cavitating Inducer in Liquid Nitrogen

For experimental investigations of the thermodynamic effect on a cavitating inducer, it is nesessary to observe the cavitation. However, visualizations of the cavitation are not so easy in cryogenic flow. For this reason, we estimated the cavity region in liquid nitrogen based on measurements of the pressure fluctuation near the blade tip. We focused on the length of the tip cavitation as a cavitation indicator. Comparison of the tip cavity length in liquid nitrogen (80 K) with that in cold water (296 K) allowed us to estimate the strength of the thermodynamic effect

Thermodynamic Effect on Subsynchronous Rotating Cavitation and Surge Mode Oscillation in a Space Inducer

The relationship between the thermodynamic effect and subsynchronous rotating cavitation was investigated with a focus on cavity fluctuations. Experiments on a three-bladed inducer were conducted with liquid nitrogen at different temperatures (74, 78, and 83 K) to confirm the dependence of the thermodynamic effects. Subsynchronous rotating cavitation appeared at lower cavitation numbers in liquid nitrogen at 74 K, the same as in cold water. In contrast, in liquid nitrogen at 83 K the occurrence of subsynchronous rotating cavitation was suppressed because of the increase of the thermodynamic effect due to the rising temperature. Furthermore, unevenness of cavity length under synchronous rotating cavitation at 83 K was also decreased by the thermodynamic effect. However, surge mode oscillation occurred simultaneously under this weakened synchronous rotating cavitation. Cavity lengths on the blades oscillated with the same phase and maintained the uneven cavity pattern. It was inferred that the thermodynamic effect weakened peripheral cavitation instability, i.e., synchronous rotating cavitation, and thus axial cavitation instability, i.e., surge mode oscillation, was easily induced due to the synchronization of the cavity fluctuation with an acoustic resonance in the present experimental inlet-pipe system.

Influence of Thermodynamic Effect on Blade Load in a Cavitating Inducer

Distribution of the blade load is one of the design parameters for a cavitating inducer. For experimental investigation of the thermodynamic effect on the blade load, we conducted experiments in both cold water and liquid nitrogen. The thermodynamic effect on cavitation notably appears in this cryogenic fluid although it can be disregarded in cold water. In these experiments, the pressure rise along the blade tip was measured. In water, the pressure increased almost linearly from the leading edge to the trailing edge at higher cavitation number. After that, with a decrease of cavitation number, pressure rise occurred only near the trailing edge. On the other hand, in liquid nitrogen, the pressure distribution was similar to that in water at a higher cavitation number, even if the cavitation number as a cavitation parameter decreased. Because the cavitation growth is suppressed by the thermodynamic effect, the distribution of the blade load does not change even at lower cavitation number. By contrast, the pressure distribution in liquid nitrogen has the same tendency as that in water if the cavity length at the blade tip is taken as a cavitation indication. From these results, it was found that the shift of the blade load to the trailing edge depended on the increase of cavity length, and that the distribution of blade load was indicated only by the cavity length independent of the thermodynamic effect.

Cavitation erosion of silver plated coating at different temperatures and pressures

Cavitation often occurs in inducer pumps used for space rockets. Silver plated coating on the inducer liner faces the damage of cavitation. Therefore, it is important to study about the cavitation erosion resistance for silver plated coating at several operating conditions in the inducer pumps. In this study, the cavitation erosion tests were carried for silver plated coating in deionized water and ethanol at several liquid temperatures (273K–400K) and pressures (0.10MPa–0.48MPa). The mass loss rate is evaluated in terms of thermodynamic parameter Σ proposed by Brennen [9], suppression pressure p–pv (pv: saturated vapor pressure) and acoustic impedance ρc (ρ: density and c: sound speed). Cavitation bubble behaviors depending on the thermodynamic effect and the liquid type were observed by high speed video camera. The mass loss rate is formulated by thermodynamic parameter Σ, suppression pressure p–pv and acoustic impedance ρc.

Theromdynamic Effect on a Cavitating Inducer in Liquid Nitrogen

For experimental investigations of the thermodynamic effect on a cavitating inducer, it is neccesary to observe the cavitation. However, visualizations of the cavitation are not so easy in cryogenic flow. For this reason, we estimated the cavity region in liquid nitrogen based on measurements of the pressure fluctuation near the blade tip. The degree of the thermodynamic effect was found to increase with the increase of the cavity length of the tip cavitation. The estimated temperature depression caused by vaporization increased rapidly when the cavity length extended over the throat. In addition, the estimated temperature inside the bubble nearly reached the temperature of the triple point when the pump performance deteriorated.