INLET DISTORTION GENERATED FORCED RESPONSE OF A LOW-ASPECT-RATIO TRANSONIC FAN

This paper describes a portion of an experimental and computational pr ogram (ADLARF), which incorporates, for the first time, measurements o f all aspects of the forced response of an airfoil row, i.e., the flow defect, the unsteady pressure loadings, and the vibratory response. T he purpose of this portion was to extend the knowledge of the unsteady aerodynamics associated with a law-aspect-ratio transonic fan where t he pow defects were generated by inlet distortions. Measurements of sc reen distortion patterns were obtained with total pressure rakes and c asing static pressures. The unsteady pressure loadings on the blade we re determined from high response pressure transducers. The resulting b lade vibrations were measured with strain gages. The steady flow was a nalyzed using a three-dimensional Navier-Stokes solver while the unste ady flow was determined with a quasi-three-dimensional linearized Eule r solver. Experimental results showed that the distortions had strong vortical, moderate entropic, and weak acoustic parts. The three-dimens ional Navier-Stokes analyses showed that the steady flow is predominan tly two-dimensional, with radially outward flow existing only in the b lade surface boundary layers downstream of shocks and in the aft part of the suction surface. At near resonance conditions, the strain gage data showed blade-to-blade motion variations and thus, linearized unst eady Euler solutions showed poorer agreement with the unsteady loading data than comparisons at off-resonance speeds. Data analysis showed t hat entropic waves generated unsteady loadings comparable to vortical waves in the blade regions where shacks existed.