Effects of Reynolds number on boundary layer and wake development of embedded turbine vane stages

Abstract

To address the aerodynamic challenges associated with low-Reynolds-number operation typical of high-altitude cruise conditions in aero-engines, this paper presents an experimental investigation—conducted on a large-scale, low-speed, multi-stage axial turbine facility—in which both the velocity triangles and the reduced wake-passing frequency were held constant. Synchronized hot-film measurements were conducted on the blade surface, and the dynamic flow field at the second-stage stator (S2) exit plane was acquired using a triple- and hot-wire probe. The study examines the effects of Reynolds number (Re = 7.4 × 104 and Re = 8.5 × 104) on the attached-flow transition and wake mixing characteristics of the S2 suction surface. The results indicate that at the lower Reynolds number, the thickened boundary layer and enhanced viscous effects lead to shear sheltering of external disturbances, resulting in a delayed transition onset and attenuated wall shear stress fluctuations. Consequently, the merging and evolution of turbulent spots are restricted, causing the calmed regions at the trailing edge to exhibit stronger intermittency. This process leads to wake broadening, an elevation of global turbulence levels, and a significant increase in velocity deficit magnitude (>1.5%), ultimately resulting in a significantly deeper and wider exit wake profile, indicative of increased aerodynamic loss.