ロケットエンジン用ターボポンプの入口配管の音響効果を考慮したキャビテーションサージの一次元解析（第3報，非線形要素による周波数の不連続変化）
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The cavitation surge is a kind of instability phenomenon generated in a liquid rocket engine, and it is known that when the inlet pressure of the turbopump of the engine is decreased, the frequency of cavitation surge continuously varied. On the other hand, it was observed in a turbopump test conducted in JAXA that the frequency of cavitation surge discontinuously decreased when the inlet pressure was decreased. Aiming at explaining this curious phenomenon, we conducted the linear analysis using the frequency-domain method and found that this phenomenon was a kind of self-excited vibration coupling the cavitation characteristics with the acoustic resonance of the inlet pipeline. However, the linear analysis could not simulate the phenomenon that a frequency of standing wave changed to the other mode at a certain inlet pressure. Therefore, we conducted the nonlinear analysis using the one-dimensional time-domain method. As a result, it was found that when the inlet pressure was decreased, the damping effect became larger in the higher frequency oscillation because of nonlinear factors. Consequently, the oscillation of higher frequency was intensely weakened and the oscillation of lower one appeared instead.