The role of porous structure on airfoil turbulence interaction noise reduction

Abstract

Experiments are performed to investigate the effect of porous treatment structure used at the leading edge on the aerodynamic and aeroacoustic characteristics of a National Advisory Committee for Aeronautics (NACA) 0012 airfoil. Three different triply periodic minimal surface porous structures of constant porosity are studied to explore their effect on the flow field and the relationship between airfoil response and far-field noise. The results show that the ratio between the porous structure pore size and the length scale of the turbulent flow plays an important role in the noise reduction capability of a porous leading edge. Changes to the turbulent flow properties in the vicinity of the airfoil are assessed to characterize the contributing physical behavior responsible for far-field noise manipulation. Velocity field analysis in front of the leading edge demonstrates a pronounced difference among porous structures. Furthermore, close to the airfoil surface and off from the stagnation line, all porous leading edges demonstrate a marked reduction in the low-frequency content of the velocity fluctuations. These results demonstrate the importance of the airfoil leading edge region and not just the stagnation line. The strong link evident in pressure–velocity coherence analysis of the solid airfoil is broken by the introduction of the porous leading edge. Furthermore, the porous leading edges reduce the near-field to far-field pressure coherence in both magnitude and frequency range.