A Feasibility Study of Riblet for Aeroacoustics Applications

Although the use of finlet, serration or porous surface has been shown a good level of success in reducing aerofoil trailing-edge noise, they are largely incompatible to the otherwise streamlined aerofoil body. This paper is a feasibility study to investigate the riblet, which has so far been quite successful as a drag-reducing device, for its potential to reduce the turbulent pressure sources that are important for aerofoil self-noise radiation. The completed results show that the riblet used in the current study can reduce the skin-friction coefficient, as well as the turbulence-intensity in the boundary-layer profiles. In addition, the turbulence structures in the convective field can be dissipated more rapidly when crossing the riblet surface. It is also found that (1) the riblet produces a slight reduction of the wall-pressure power spectral density level at the low and high frequency ranges, but experiences an increase at the mid frequency, (2) the riblet can reduce the lateral turbulence coherence length-scale across a large frequency range. The product of these two hydrodynamic sources represents an important mechanism for the radiation of the trailing-edge self-noise, whose low and high frequency ranges are found to be sensitive to the riblet effect where reduction can occur.