EFFECTS OF SOUND ABSORBING WALL ON BLADE ROW FLUTTER AND SOUND GENERATION UNDER INTERACTION OF MULTIPLE BLADE ROWS

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An unsteady lifting surface theory was developed for a model of three blade-rows with vibrating blades, to account for the simultaneous effects of adjacent blade rows situated upstream and downstream. 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 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 simultaneous influences of the upsteam and downstream neighboring blade rows on unsteady loading caused by blade vibration. The effects of two downstream blade rows and two-upstream blade rows are also investigated.It is a common understanding that interaction of stator vanes with oncoming rotor wakes is the primary source o … More f the fan tone noise of turbofan engines. A prediction scheme on the basis of genuine 3-dimensional lifting surface theory including the effect of mutual aeroacoustic interaction between the rotor and the stator was developed. The scheme was further modified into a hybrid scheme, which deals with vortical interaction of stator vanes with oncoming vortical wake disturbances from the upstream rotor on the basis of CFD technique and deals with aeroacoustic interaction of the two blade rows on the basis of the unsteady lifting surface theory. A computation program was coded to predict the generated sound power.The above models were further generalized to include the effect of the sound absorbing walls, and the comprehensive models were mathematically formulated.New findings are summarized as follows.(1) The simultaneous influence of the upstream and downstream blade rows can not be accounted for by a simple superposition of interactions between two blade rows. The effect of the next blade row but one is also substantial in the case of very short distances between blade rows.(2) The effect of the acoustic interaction between the rotor and the stator on the radiated sound power is very substantial. The effect heavily depends on the harmonic number of the blade passing frequency. Less