Investigation of transitional flows on compressor blades in cascade

Abstract

Flow around polished second-generation controlled-diffusion blades in cascade set at their design inlet flow angle was investigated at various Reynolds numbers using static pressure measurements, five-hole probe surveys, twocomponent laser Doppler velocimetry (LDV), computational fluid dynamics and flow visualization. A suction-side separation bubble formed at Reynolds number, based on chord length, of 203,000 and collapsed by a Reynolds number of 393,000. Five-hole probe surveys characterized the blade-row inlet and outlet flow and showed the loss coefficient had a maximum value of 0.030 at a Reynolds number of 203,000 and a minimum of 0.012 at a Reynolds number of 400,000. The suction-side separation bubble was completely documented with LDV. The boundary layer was found to undergo laminar separation at 55 percent axial chord, transitioned in the boundary layer and re-attached turbulent by 67 percent axial chord. A quasi three-dimensional, Reynolds-Averaged Navier-Stokes, computational fluid dynamics model was created and accurately predicted the suction-side separation bubble and boundary layer transition inside the bubble. Flow visualization verified the transitional behavior of the separation bubble and showed the separation point was steady while the reattachment point was turbulent.