Design Support Numerical Code for Stall Flutter Analysis.

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This study aims to develop a numerical calculation code which enables us to predict the unsteady aerodynamic characteristics of the stalled compressor and turbine cascades as well as their stall flutter limits.For this end, the numerical code which authors have used so far to analyze the unsteady flow of rotating stall was extended so that it can deal with the flow through the cascades, of which the blades oscillate rotationally or translationally.With use of this code, a series of numerical analyzes of the stalled flow through a typical compressor cascade with each blade oscillating rotaionally around the mid-point of the mean camber line was carried out. The reduced frequency and the inter-blade phase angle were changed in wide varieties and it was found that the unsteady exciting moment of the stall flutter was closely connected with the propagation of rotating stall along the cascade. The numerical code was also applied to the analysis of oscillating turbine cascades. Rotational oscillation of a nozzle cascade with large deflection angle, and translational oscillation of a rotor cascade with high stagger and low turning angles were selected as examples for the analysis. A series of unsteady aerodynamic characteristics were obtained for wide range of unsteady oscillation parameters.Further, a cascade wind-tunnel test of the same rotationally oscillating cascade as used in the numerical analysis of the compressor cascade was performed. Unsteady pressure distributions on the oscillating blade surface were measured, and the unsteady aerodynamic works given to the blades were calculated. The experimental results agreed well with those predicted by the numerical calculation.