Investigation on Suppression Mechanism of Rotating Cavitation in Inducers

在LE-7发动机的液氧泵诱导器和包括液氧泵在内的流体系统中，分别出现了旋转汽蚀和汽蚀喘振现象，通过对诱导器上游壳体的简单改造，几乎完全抑制了这两种现象。然而，这种抑制的机制还不能完全解释。本文研究了旋转空化的抑制机理以及旋转空化和空化涌浪的共同特征。首先，用三种不同尺寸的诱导器罩进行了实验，得到了非定常空化流动的模式图，其中包括改进型和与LE-7型泵诱导轮尺寸相近的诱导器。其次，利用高速胶片和粒子图像测速仪(PIV)对诱导器上游的流动进行了观察。结果表明，改装后的诱导器壳体增加了诱导器入口尖端附近的回流，回流增加了空穴体积，从而增加了空化柔度。空化柔度的增加也被认为是抑制旋转空化的主要原因。第三，从实验和理论分析两个方面阐明了旋转空化和空化浪涌是非常相似的现象。此外，考虑到质量流量增益因子的相位延迟，可以解释相当高的空化涌动频率，这是旋转空化和空化激增的主要原因。第四，证实了包括空化气泡影响的低温两相流分析可以应用于诱导器的非定常内部流动。

Rotating cavitation and cavitation surge occurred in a liquid oxygen pump inducer of the LE-7 engine and in a fluid system including the pump, respectively, Both the phenomena were almost completely suppressed by a simple modification of the inducer upstream housing. However, the mechanism of the suppression could not be fully explained. In this study suppression mechanism of the rotating cavitation and the common characteristics between rotating cavitation and cavitation surge were investigated.First, an experiment was performed using three inducer housings including a modified one and an inducer which had almost similar dimensions of the LE-7 pump inducer to obtain a map of modes of unsteady cavitating flows. It was clarified that the modified inducer housing shifted the region in which the rotating cavitation occurred to higher flow rates.Second, another experiment was conducted using a high speed filming and a particle image velocimeter(PIV) to observe the flow upstream of the inducer. It was clarified that the modified inducer housing increased back flow near the tip of the inducer inlet and that the back flow increased the cavity volume, which resulted in the increase of cavitation compliance. The increase of cavitation compliance is also considered to be a main cause of suppressing the rotating cavitation.Third, it was also clarified that rotating cavitation and cavitation surge was a very similar phenomena from both the experimental and theoretical analyses. Furthermore, fairly high frequency of the cavitation surge could be explained by taking into consideration the phase delay of the mass flow gain factor which is a major cause of both the rotating cavitation and cavitation surge.Fourth, it was confirmed that an analysis of a cryogenic two-phase flow which includes the effect of cavitating bubbles could be applied to the unsteady internal flow of an inducer.