Vibratory Forcing Functions Produced by Nonuniform Cascades

A method is developed to predict the steady, two-dimensional incompressible flowfield through tandem cascades or multibody cascade geometries. The technique is adapted from the classical Douglas-Neumann method, in which a superposition of singularities is used to simulate the cascade geometries. The method is used to analyze the self-induced potential field interaction of a stator cascade with a finite thickness strut cascade behind it or integral within it, such as occurs in fan ducts and intermediate cases of large gas-turbine engines. The calculation predicts the magnitude and location of the nonuniform pressure distortion, which would be imposed on an upstream engine component, for a variety of cascade designs. Such a distortion is known to produce resonant stresses in an upstream rotor. Experimental corroboration of the analysis is presented for a cascade operating at M_∞ = 0.49. Sensitivity of the distortion pattern to small strut restaggering is calculated and compared to test data.