Passive control of hub-corner separation/stall using axisymmetric-hub contouring

Abstract

Numerical simulations were performed to investigate the forming mechanism of the compressor/fan hub-corner separation/stall. Taking the small-scaled vortex in the detached regions into account, scale adaptive simulation model coupled with shear stress transport model (SAS–SST turbulence model) does well in capturing the flow structures in the compressor. At near stall condition, low-momentum stall cell originates from the leading edge of the stator near hub, contributes to the greater turning angle at the suction side because of endwall viscosity, rolls, and lifts up in spanwise direction. The same then interacts with the wake in the downstream passage of stator, nearly taking up the whole passage downstream. Three vortex centres are generated at the hub induced by the boundary layer separation flow, one near the stator leading edge, a second one at the blade trailing edge near the suction side, and a third one near the middle passage, and further swirled up to the blade suction surface which can be recognized as thepassage vortex developed by the radial and circumferential pressure differences. Axisymmetric-hub contouring (a type of passive flow control techniques) has resulted in performance improvement of the compressor. Main contribution of performance enhancement is attributed to the suppression of hub-corner separation. Significant influence of axisymmetric contouring has been found on boundary layer separation structures near hub and passage vortex, which affects the formation and development of hub-corner stall.