The Measurement of Boundary Layers on a Compressor Blade in Cascade: Part 2—Suction Surface Boundary Layers

Using the facility described in Part 1 [29], eleven detailed velocity and turbulence intensity profiles are obtained on the suction surface of a double circular arc blade in cascade. At the measured incidence angle of 5 deg, transition through a leading edge separation bubble occurs before 2.6 percent chord. A continuing recovery from this leading edge separation is apparent in the measured boundary layer profiles at 2.6 and 7.6 percent chord. Recovery appears to be complete by 12.7 percent chord. The data then illustrate the evolution of the nonequilibrium turbulent boundary layers as they approach a second region of separation. Following the criteria established by Simpson et al. [1], we find that intermittent separation occurs near 60 percent chord while detachment occurs at 84.2 percent chord. Comparison between the measured profiles and the sublimation visualization studies indicates that the flow visualization is signaling the location of incipient detachment (1 percent instantaneous backflow). Measured profiles are also considered in light of similarity techniques for boundary layers approaching separation. Outer region similarity is shown to vanish for profiles downstream of detachment.