A surface flow visualization study of boundary layer behavior on the blades of a solid-wall compressor cascade at high angles of attack

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Virginia Polytechnic Institute and State University

The oil-film surface flow visualization technique was applied to circular arc compressor blades in a solid wall, high aspect ratio cascade for the purpose of describing the transition from corner stall to full blade stall, and the blade surface flow under fully stalled conditions. Photos of the visualizations for three stagger angles are presented and analyzed. A map quantitatively describing the observed boundary layer development at midspan is presented.

The most interesting discovery of the work showed the suction surface flow to be essentially two-dimensional, in the geometric sense, preceding and following the transition to a fully separated flow at the leading edge. Corner stall was the observed three-dimensional mechanism prior to full stall. For fully-stalled conditions, the three-dimensional mechanism took the form of recirculating flow regions at the blade ends. Complete separation at the leading edge occurred at lower angles of attack for the higher stagger angles. Special blade oil-flow tests were conducted to evaluate Reynolds number and tip clearance effects on boundary layer development.

The experimental work was done as part of a larger research program aimed at measuring and predicting the stalled performance of a compressor cascade.