Effect of Reynolds number on separation bubbles compressor blades in cascade

A detailed experimental investigation of second-generation, controlled-diff usion, compressor stator blades at an off-design inlet-Row angle was perfor med in a low-speed-cascade wind tunnel primarily using laser Doppler veloci metry (LDV), The object was to characterize the flowfield in the Reynolds n umber range of 2.1-6.4 x 10(5) and to obtain LDV measurements of the suctio n surface boundary-layer separation that occurred near midchord. Surface Ro w visualization showed that at the low Reynolds number the midchord separat ion bubble started laminar and reattached turbulent within 20% chord on the suction side of the blade. The extent of the bubble compared very well wit h the measured blade surface pressure distribution, which showed a classica l plateau and then diffusion in the turbulent region. LDV measurements of t he flow reversal in the bubble were performed. At the intermediate Reynolds number, the boundary layer was transitional upstream of the separation bub ble that had decreased significantly in size (down to 10% chord). At the hi ghest Reynolds number, the Row was turbulent from close to the leading edge , and three-dimensional Row reversal as a result of endwall effects appeare d at approximately 80% chord, These data, particularly the low Reynolds num ber data, are an excellent test case for either large-eddy simulation or di rect numerical simulation of cascade flowfields.