A Study on the Relation between Stall Flutter and Rotating Stall

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The aim of this study is to understand the relation between the stall flutter and the rotating stall by means of numerical simulations.In the first year of the study, the numerical method for the analysis of rotating stall in rigid cascades was extended so that it can treat the cases where the cascade blades oscillate with small amplitudes. A typical cascade of NACA-65CA (30) 10 compressor blades was selected as a calculation objective, and its unsteady aerodynamic characteristics were analyzed when each blade was oscillating rotationally around the center of each camber line with various oscillation parameters. Rotating stall occurred in these cascades as well if the inlet flow angle was large, and further, when the phase velocity of blade oscillation coincided with the propagation velocity of the rotating stall, the both phenomena synchronized and the blade oscillation was excited strongly, i.e., the stall flutter occurred.In the second year, a series of numerical simulation was carried out for the same cascade with increasing the inlet flow angle step by step around the stalling inlet flow angle, in order to see the relation between the occurrence of stall flutter and the appearance of rotating stall. When the inlet flow angle is comparatively low, neither the stall flutter nor the rotating stall occurred. When the inlet flow angle was increased slightly, it became possible for the rotating stall to appear depending on oscillation conditions of the blades. In this situation, although the synchronization of the both phenomena as mentioned before was not seen, the excitation of the blade oscillation by a "broader sense of stall flutter" became possible. When the inlet flow angle was increased further beyond, it was found the situation was continued to that described in the first years' result.