EFFECTS OF NEIGHBORING BLADE ROW ON SUPERSONIC CASCADE FLUTTER

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An unsteady lifting surface theory was developed for contra-rotating annular blade rows with vibrating blades. A program was coded to compute unsteady aerodynamic force and work on blades for specified frequency, inter-blade phase angle and other design parameters. The program is comprehensive, and it can deal with various combinations of blade rows, i.e., combinations of subsonic and subsonic blade rows, supersonic and supersonic blade rows, and subsonic and supersonic blade rows. The validity of the program was confirmed by making a comparison for a model condition between the results from the present program and those of CFD Euler code computation conducted by Professor K.C.Hall of Duke University. Both results were in complete agreement.Parametric studies were conducted to investigate the influence of the neighboring blade rows on unsteady loading caused by blade vibration.A computation program was coded to determine the critical condition of occurrence of coupled bending-torsion f … More lutter, which utilizes the above mentioned program as a subprogram to calculate unsteady aerodynamic force terms in flutter equations. The influence of the neighboring blade row on the flutter boundaries was investigated.New findings are summarized as follows.(1)Vibrating subsonic blade row : Unsteady aerodynamic work on vibrating blades, critical flutter velocity, critical flutter frequency and flutter mode are substantially influenced by the presence of a neighboring blade row in cases where the fundamental acoustic duct mode generated from the vibrating blade row is cut-on. On the other hand in cases where the fundamental acoustic duct mode is cut-off, the influence of the neighboring blade row is essentially small unless the blade row gap is very small.(2)Vibrating supersonic blade row : Unsteady aerodynamic work on vibrating blades, critical flutter velocity, critical flutter frequency and flutter mode are very sensitive to parametric change near the resonance points of low order acoustic duct modes. The behaviors of the variations with the parametric change are heavily influenced by the presence of the neighboring blade row. Less