NUMERICAL SIMULATION OF FLAP SIDE-EDGE NOISE REDUCTION USING POROUS MATERIAL TREATMENT

The flap side-edge plays an important role in the generation of airframe noise, especially at the stage of landing. Previous studies have shown that a porous treatment has great potential to reduce the flap side-edge noise over a wide range of frequencies. However, the physics responsible for this noise reduction remains in further discussion. In this study, detached eddy simulations were carried out to reveal the effect of porous treatment on the flow field around an isolated flap-side edge. It is demonstrated that the porous treatment has a great impact on the vortex initiation and roll-up processes. The fusion process of the double vortex is significantly inhibited and a decrease in the pressure fluctuations occurred on the flap side-edge surface. The far-field noise results claimed that the porous material treatment can achieve about 4 dB noise reduction. The influence of the porous treatment area was also discussed in this study. The numerical result shows that with the increasing porous region spanwise length, flow separation on the flap surface occurred, which lead to a reduction in aerodynamic performance. This phenomenon reminds us that the porous treatment area should be carefully considered during the low-noise design stage to balance the aerodynamic performance and the aeroacoustics performance.