A new strategy on porous trailing edges for self-noise reductions

Extensive research efforts in the aeroacoustics community have firmly established the benefits of porous trailing edges to achieve low-noise radiation for aerofoil. This paper investigates a novel and simplistic pore-arrangement at the trailing edge for noise reduction. The research entails several 3D-printed interchangeable trailing edges, each of which has only a single-row of porous-array at a pre-determined distance upstream of the trailing edge. This type of treatment is expected to facilitate a frequency-targeting capability based on the wave interference mechanism. More specifically, it can cause a phase-cancellation between the pressure waves emanating from two sources (i.e. the porous-array and the trailing edge) that are physically displaced in a longitudinal direction. If the acoustic sources are 180 degrees out of phase, destructive interference occurs between the two scattering sources leading to a cancellation of noise. Eighty-one trailing edges that have different combinations of streamwise separation distance between the two sources, pore size and spanwise separation distance between the pores were tested. The results show that many of these trailing edges can indeed achieve low-noise radiation. Near wake measurements have established that the single-row of porous array will not alter the boundary layer significantly. Therefore, the observed noise reduction is solely based on the acoustic interference mechanism only.