Noise reduction using combined trailing edge and leading edge serrations in a tandem airfoil experiment

This work reports the noise reduction obtained using simultaneously serrated trailing edges and serrated leading edges in a tandem airfoil con guration. Two types of serrated trailing edge treatments are applied to the upstream airfoil, i.e., a sawtooth serration and a slitted sawtooth serration. The leading edge serrated airfoil was designed and manufactured by ONERA. Broadband noise reductions of between 5 dB and 8.5 dB are reported. It is shown over most of the frequency range that overall noise radiation is dominated by interaction noise, while trailing edge noise dominates the high frequency power spectrum at low mean ow velocity. Therefore, the overall noise reduction is dominated by the reductions in interaction noise, and particularly by the reduction of the downstream airfoil response R(f) due to leading edge serrations. However, additional reductions of the overall noise radiation of up 3.5 dB are provided by the use of the slitted sawtooth trailing edge rather than the sawtooth trailing edge on the upstream airfoil, at the high ow velocity U0 = 80m=s. This is shown to be most likely due to modi cations of the wake parameters, i.e., notably a faster decay of the turbulence intensity behind the slitted sawtooth trailing edge.