Investigation of Second Generation Controlled-Diffusion Compressor Blades in Cascade.

Abstract : Detailed experimental investigation of second generation controlled-diffusion compressor stator blades at design inlet-flow angle was performed in a low-speed cascade wind tunnel using various experimental methods. Surface pressure measurements were obtained using three instrumented blades, from which coefficients of pressure were calculated. Laser-Doppler velocimetry was used to characterize the flow in the inlet, in the passage between two blades, in the boundary layer of the blades, and in the wake. A five-hole pressure probe was used to determine the loss coefficient and the axial-velocity-density ratio of the flow through the cascade. Although the blades produced significant lift, separated flow was discovered on the suction side of the blades at approximately fifty percent axial chord, which showed that the design was not totally successful. All the experimental measurements were performed at an inlet flow Mach number of 0.22 and a Reynolds number, based on chord length, of 640,000. Experimental blade-surface pressure coefficients were compared with values predicted using a computational fluid dynamics code. These initial predictions did not match well with the experimental results.