Reynolds number effects on the aerodynamics of compact axial compressors

Abstract

The performance of a compact axial compressor is limited by increased viscous losses and reduced flow turning caused by operation at low Reynolds number (Re). This paper aims to develop improved understanding of the loss variation with Re in such a compressor. Experiments of a scaled-up single stage axial compressor have been conducted across a range of Re of 104 - 105. The flow field has been measured at the rotor inlet, rotor exit and stator exit using detailed area traverses with a miniaturised five-hole probe. In addition, three-dimensional computations of the same compressor stage have been conducted to investigate how effective steady fully turbulent RANS CFD, with the Spalart Allmaras turbulence model, is for this low Re regime. As expected, the measured loss decreased with increasing Re for both the stator and rotor. This variation in loss was found to be dominated by changes in three-dimensional flow features. In the rotor, there is high tip loss and a hub separation that grows at low Re, which CFD does not predict. The stator has high hub loss, which the CFD over-predicts, particularly at low flow coefficients. The results demonstrate that the fully turbulent solver used can be used to guide the design but cannot predict the detailed aerodynamic loss sources or the impact of Reynolds number variations.