Tsujimoto 教授是国际著名的流体力学和流体机械专家，在流动非稳定机理、空化非稳定现象等研究领域享有盛誉。Tsujimoto教授是AIAA、ASME、日本机械学会的资深会员、编辑委员会成员和理事。主要国际学术兼职：1）Chairman of US-Japan seminar on Abnormal Phenomena in Turbomachinery (sponsored by NSF and JSPS), 1998；2）Scientific Committee member of The 8^th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery, 2000-2009；3）Associate Editor of ASME Journal of Fluids Engineering, 2000-2007；4）Editor of International Journal of Rotating Machinery, 2001-；5）Editor of International Journal of JSME, 2001-；6）Chairman of the 5th International Symposium on Cavitation, 2003；7）Chair of Publication Committee, the 23^rd IAHR Symposium on Hydraulic Machinery and Systems.

 

This topic focuses on the cause of cavitation instabilities such as cavitation surge and rotating cavitation. To get fundamental understanding, one dimensional analysis is made first. The result shows that the cavity volume decrease associated with the increase of flow rate is the main cause of cavitation instabilities. However, the analysis predicts also a mode of rotating cavitation in which the cavitated region rotates in the direction opposite to the impeller, which is not observed frequently. To overcome this difficulty, a two dimensional stability analysis is made assuming a closed blade surface cavity model. The results show that various modes of cavitation instabilities start to occur when the cavity length becomes about 65% of the blade spacing. This is because the local flow near the cavity trailing edge starts to interact with the leading edge of the next blade at this cavity length. Although this result agrees with experimental observations, tip cavities are observed in experiments instead of blade surface cavitation assumed in the analysis. Then, 3-D cavitating unsteady flow CFD is made. It is shown that alternate blade cavitation and rotating cavitation start to occur when the trailing edge of tip cavity approaches the leading edge of the next blade. Although the flow with the bubbly flow model does not turn around the cavity surface, it was found that there exists a local disturbance flow towards the cavity trailing edge. This flow reduces the attack angle to the next blade and cavitation instabilities starts to occur when this local flow starts to interact with the leading edge of the next blade. In all of 1-3 dimensional analysis, the fundamental character of cavitating flow, that the cavity volume decreases when the pressure increases, plays the most important role in cavitation instabilities.