Porous geometry effects on the generation of turbulence interaction noise

Turbulence interaction noise between a turbulent inflow and an airfoil with various porous leading edges has been experimentally investigated. The effect of multiple parameters of the porous structure at the leading edge of a NACA 0012 airfoil on the aeroacoustic characteristics were investigated at a chord-based Reynolds number of 2.6 x 10^5. The airfoil was additive manufactured and has an interchangeable leading edge allowing for porous structure to occupy up to 20% of the chord. The turbulent inflow was generated by placing a grid within the contraction nozzle which does not affect the normal background noise of the wind tunnel jet. The effect of the porous leading edges were quantified by direct noise measurement and was compared to the results of a solid leading edge. It is found that far-field noise was reduced for low frequency in most cases, but incorporation of the porous material introduces a penalty of high frequency noise. An increase in the porous-occupied volume at the leading edge increases the level of surface pressure fluctuation at low frequency, and increases the level of coherence in both spanwise and streamwise direction.