Study of the numerical simulation method for unsteady cavitating flow

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Cogitating flows in cascades contain wide variety of physics, ranging from microscopic bubble dynamics to macroscopic unsteady flow. Thus experimental or theoretical analysis of such two-phase flows contains difficulties. Recently, numerical investigation is expected to become a reasonable tool, especially for application in industry. An objective of this study is to construct a practical method to analyze unsteady and unstable phenomena in cascade flow. In FY2001, we proposed a modified cavitations model based on Chen's method to deal with macroscopic flow field with unsteady cavitations and applied it to three-dimensional computation. As a result, characteristic structure such as interaction between re-entrant jet and cloud cavitations was reasonably reproduced. In FY2002, the reliability of our method was improved. Namely, the accuracy and robustness of low Mach-number assumption method and the conservation properties of non-reflection boundary condition were particularly considered. In addition, the analysis of interactive phenomena of cavitation among flow passages in two-dimensional cascade was started. In FY2003, some improvements for computational model were continued. For instance, new sub-grid scale turbulence model for the large eddy simulation (LES) on generalized curvilinear coordinate system was developed. Although it was not combined to the cavitation analysis in the term of this project, we believe it is hopeful for next development. As for the two-dimensional simulation, the two propagation modes due to the rotating cavitation and the flow separation were successfully reproduced and the result confirmed the adequacy of our method.