Effects of Loading Distribution on the Separated Transitional Flow Over Compressor Blades

Abstract

The separated transitional flow on the suction surface of three compressor airfoils, characterized by equivalent diffusion level but different loading distributions, has been investigated through large eddy simulations (LESs) at a Reynolds number of 1.5×10 5 . The baseline airfoil (V103-B) was redesigned to obtain an ultra-front-loaded (V103-UF) and an aft-loaded airfoil (V103-A). The turbulent statistics, vortex dynamics, and aerodynamic performance of the three airfoils were compared. A time-averaged laminar separation bubble (LSB) formed on the suction surface of V103-B and V103-UF. Two-dimensional spanwise vortices shed periodically and were stretched with the amplification of Kelvin-Helmholtz (K-H) instability. Finally, three-dimensional hairpin vortices broke down into small turbulent eddies near the reattachment, along with the ejection-sweeping process of the near-wall flow. For V103-A, the turbulent separated layers failed to reattach on the blade surface. As such, the spanwise vortices shed randomly due to the strong interaction with the reverse flow. Furthermore, the perturbations in the separated shear layer propagated upstream and potentially triggered an absolute instability. By comparison, the LSB was suppressed on the suction surface of V103-UF. Therefore, the turbulent fluctuations in the separated flow were weakened, which contributed to significant profile loss reduction. Conversely, the performance of V103-A was degraded by the rapid turbulence generation in the extended reverse flow region.