A new analytical model is developed for the prediction of noise from serratedtrailing-edges. The model generalizes Amiet's trailing-edge noise theory tosawtooth trailing-edges, resulting in an inhomogeneous partial differentialequation. The equation is then solved by means of a Fourier expansion techniquecombined with an iterative procedure. The solution is validated throughcomparison with finite element method for a variety of serrations at differentMach numbers. Results obtained using the new model predict noise reduction ofup to 10 dB at 90 degree above the trailing-edge, which is more realistic thanpredictions based on Howe's model and also more consistent with experimentalobservations. A thorough analytical and numerical analysis of the physicalmechanism is carried out and suggests that the noise reduction due to serrationoriginates primarily from interference effects near the trailing-edge. A closerinspection of the proposed mathematical model has led to the development of twocriteria for the effectiveness of the trailing-edge serrations, consistent butmore general than those proposed by Howe. While experimental investigationsoften focus on noise reduction at ninety degrees above the trailing-edge, thenew analytical model shows that the destructive interference scattering effectsdue to the serrations cause significant noise reduction at large polar angles,near the leading edge. It has also been observed that serrations cansignificantly change the directivity characteristics of the aerofoil at highfrequencies and even lead to noise increase at high Mach numbers.
展开▼
