A detailed experimental investigation of secondgeneration,controlled-diffusion, compressor statorblades at an off-design inlet-flow angle was performed ina low-speed cascade wind tunnel primarily using laser-Doppler velocimetry (LDV). The object of the study wasto characterize the off-design flowfield and to obtain LDVmeasurements of the suction surface boundary layerseparation which occurred near mid chord. The effect ofReynolds number on the flow separation in the regime of210,000 to 640,000 was investigated. Surface flowvisualization showed that at the low Re. no. the midchordseparation bubble started laminar and reattachedturbulent within 20% chord on the suction side of theblade. The extent of the bubble compared very well withthe measured blade surface pressure distribution whichshowed a classical plateau and then diffusion in theturbulent region. LDV measurements of the flow reversalin the bubble were performed. At the intermediate Re.no. the boundary layer was transitional before the bubblewhich had decreased significantly in size (down to 10%chord). At the highest Re. no. the flow was turbulentfrom close to the leading edge, and three-dimensionalflow reversal as a result of endwall effects appeared atapproximately 80% chord which did not reattach.
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