This study focuses upon a new permeable topology design concept as an alternative to porous metal foams, for turbulent boundary layer trailing-edge (TBL-TE) noise attenuation. The present permeable topology has unconventional characteristics with respect to the metal foams: a combination of low flow resistivity r and high form drag coefficient C. The unconventional characteristics are realized by a Kevlar-covered 3D-printed perforated structure. An experimental study featuring a NACA 0018 airfoil model with a Kevlar-covered 3D-printed TE insert at chord-based Reynolds numbers up to $\text{4}.\text{6}\times {\text{10}}^{\text{5}}$ is carried out. The airfoil with this TE insert gives a broadband TBL-TE noise reduction up to approximately 5 dB, compared to a solid TE. This reduction varies only slightly with airfoil loading (lower than 1 dB variation), in contrast to the porous metal foams (up to 3 dB variation). When comparing the variation of noise attenuation given by all the permeable materials considered, the variation is found to decrease with the increasing C. This is because C specifies the permeable material's ability to withstand the increasing pressure difference, which causes cross flow that might interfere with the noise attenuation mechanism. Additionally, the drag coefficients as well as the roughness noise of the airfoil equipped with the present TE insert are also significantly lower than those of the metal-foam TE, and are mostly negligible compared to the fully solid airfoil. Based on the findings, design guidelines for permeable TE are proposed: the permeable material shall have a combination of a low flow resistivity and a high form drag coefficient as well as a negligible surface roughness.

这项研究集中在一种新的可渗透拓扑设计概念上，以替代多孔金属泡沫，以减小湍流边界层后缘（TBL-TE）的噪声。本发明的可渗透拓扑结构相对于金属泡沫具有非常规特征：低流动电阻率r和高形式阻力系数C的组合。非常规特性是通过凯夫拉（Kevlar）覆盖的3D打印的穿孔结构实现的。一项具有NACA 0018机翼模型的实验研究，该模型具有凯夫拉覆盖的3D打印的TE插入物，基于和弦的雷诺数最大为$\text{4}。\text{6}\times {\text{10}}^{\text{5}}$完成了。与实心TE相比，带有TE插入件的机翼可将宽带TBL-TE噪声降低约5 dB。与多孔金属泡沫（最大变化3 dB）相比，这种减小仅随翼型载荷的变化而变化（小于1 dB）。当比较考虑的所有可渗透材料给定的噪声衰减变化时，发现该变化随C的增加而减小。这是因为C指定可渗透材料承受不断增加的压差的能力，该能力会导致可能会干扰噪声衰减机制的错流。另外，配备有本发明TE插入件的翼型的阻力系数以及粗糙度噪声也显着低于金属泡沫TE的阻力系数和粗糙度噪声，并且与全固态翼型相比几乎可以忽略。基于这些发现，提出了可渗透TE的设计指南：可渗透材料应具有低流动电阻率和高形式阻力系数以及可忽略不计的表面粗糙度的组合。