Basic Investigation on Rotating Cavitation

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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