Basic Investigation on Rotating Cavitation

作为实验的第一步，我们建立了LE-7液氧诱导器的缩尺模型和空化风洞，观察到了大范围运行条件下的空化不稳定性，包括旋转空化和空化浪涌。这导致了吸力性能图表中这些不稳定性的地图。此外，通过对机匣壁面非定常压力的测量，结合新开发的数据采集系统，可以直观地观察到空化在叶片间的传播过程。结果表明，在…计算中适当考虑空泡增长效应，可以用二维涡计算模拟空化的发展过程更多的挑战。在此基础上，我们计划建立叶尖泄漏空化的三维模型，用于评估叶尖泄漏空化的非定常特性。为了评价叶片表面和叶尖泄漏空化的非定常特性，我们建立了振动箔试验装置。作为初步实验，完成了固定翼片的空化试验。研究发现，在常规的局部空化不稳定性的基础上，还会出现频率更高的空化不稳定性。通过对旋转空化的非线性模拟发现，进口压力降低导致的空化柔度增大是决定旋转空化幅度的一个因素。对平行板之间或同心圆柱体之间的三维驱动盘的分析表明，几何形状和腔体的三维效应对基跨方向的振型影响不大。有限螺距空化叶栅分析的二维稳定性分析表明，在这种更详细的流动模型中，旋转空化是不存在的，从而从不同的角度再次证实了旋转空化本质上是一种具有正质量流量增益因子的二维局部流动不稳定性。然而，详细的理论分析显示了其他类型的旋转空化的可能性，这些空化还没有在实验上被发现。对这些模式的研究被作为未来的问题继续进行。较少

This support enabled us to carry out three types of experiments and five types of theoretical analyzes, each of them resulting in valuable contributions for the understanding of rotating cavitations.As the first step of experiments, a scale model of LE-7 LOX inducer and a cavitation tunnel were built and cavitation instabilities including rotating cavitation and cavitation surge were observed in a wide rnage of operating conditions. This resulted in a map of those instabilities in the suction performance chart. In addition, the propagation of cavity from one blade to another could be visualized from a casing wall unsteady pressure measurement combined with a data acquisitions system newly developed for this purpose.The cavitation in a two dimensional transient tip leakage flow was observed as a basic study of tip leakage cavitation. It was found that the growth of cavitation can be simulated by a 2-D vortex calculation if the cavity growth effect is properly incorporated in the calcula … More tion. Based on this calculation, we are planning to build a 3-D tip leakage cavitation model which can be used to evaluate the unsteady characteristics of tip leakage cavitation.To evaluate the unsteady characteristies of blade surface and tip leakage cavities, and oscillating foil test device was built. As a preliminary experiment, a cavitation test with fixed foil has been finished. It was found that a higher frequency cavitation instability occurs as well as the conventional partial cavitation instability. This device will be used to study the cavitation instability problems as well as the original purpose.It was found by a non-linear simulation of rotating cavitation that the increase of cavitation compliance due to decrease of inlet pressure is a factor to the determine the amplitude of rotating cavitation. Three-dimensional actuator disk analyzes between two parallel plates or between two concentric circular cylinders showed that the 3-D effects of the geometry and cavity have little effects on fundamental span wise mode. A 2-D stability analysis of finite pitch cavitating cascade analysis showed that rotating cavitations disoccur in such a more detailed flow model.Thus it was reconfirmed that rotating cavitation is basically a 2-D local flow instability due to positive mass flow gain factor from various prints of view. However the detailed theoretical analyzes showed the possibilities of other types of rotating cavitations which have not been experimentally found. Studies of those modes were carried over as the future problems. Less