Effects of Reynolds number and loading distribution on the aerodynamic performance of a high subsonic compressor airfoil

The laminar-turbulent transition process on the compressor blade surface is often induced by the laminar separation flow at low Reynolds number (Re). In the present study, numerical simulations were conducted to investigate the structure of the laminar separation bubble and its effects on the profile loss of a high subsonic compressor airfoil under different Re conditions, and the mechanism for the performance deterioration of compressor airfoil at low Re was clarified. Besides, the airfoil was redesigned to obtain a series of airfoils with different loading distributions, and the aerodynamic performance of these airfoils was compared and analyzed in detail. According to the simulation results, the laminar separation bubble mainly determined the loss generation process of a compressor airfoil. When Re decreased from 12 x 10(5) to 1.5 x 10(5), the laminar separation bubble on the suction surface grew thicker and the length was increased by 11.2% of the axial chord. As such, the reversed flow inside the laminar separation bubble became more obvious and the turbulence level downstream of the maximum thickness of laminar separation bubble was increased. Also, the growth in the turbulent boundary layer was enhanced, causing more serious flow blockage and wake mixing. According to the Denton's profile loss model, the larger trailing edge loss caused by the stronger displacement effect of laminar separation bubble was supposed to be the main reason for the performance deterioration of compressor airfoil under low Re conditions. The ultra-front loading distribution for airfoil has the possibility to suppress or even eliminate the negative effect of laminar separation bubble, and the profile loss was decreased by 26.7% at Re = 1.5 x 10(5); however, the less significant performance improvement was observed at some higher Re. Moreover, the ultra-front loaded airfoil was less sensitive to the inlet turbulence level and the superiority still holds even at some supercritical conditions.