Hedayati Reza, Rubio Carpio Alejandro, Luesutthiviboon Salil, Ragni Daniele, Avallone Francesco, Casalino Damiano, van der Zwaag Sybrand
Novel Aerospace Materials group, Faculty of Aerospace Engineering, Delft University of Technology (TU Delft), Kluyverweg 1, 2629 HS Delft, The Netherlands.
Section Aircraft Noise & Climate Effects (ANCE), Faculty of Aerospace Engineering, Delft University of Technology (TU Delft), Kluyverweg 1, 2629 HS Delft, The Netherlands.
Materials (Basel). 2019 Apr 2;12(7):1087. doi: 10.3390/ma12071087.
Studies on porous trailing edges, manufactured with open-cell Ni-Cr-Al foams with sub-millimeter pore sizes, have shown encouraging results for the mitigation of turbulent boundary-layer trailing-edge noise. However, the achieved noise mitigation is typically dependent upon the pore geometry, which is fixed after manufacturing. In this study, a step to control the aeroacoustics effect of such porous trailing edges is taken, by applying a polymeric coating onto the internal foam structure. Using this method, the internal topology of the foam is maintained, but its permeability is significantly affected. This study opens a new possibility of aeroacoustic control, since the polymeric coatings are temperature responsive, and their thickness can be controlled inside the foam. Porous metallic foams with pore sizes of 580, 800, and 1200 μm are (internally) spray-coated with an elastomeric coating. The uncoated and coated foams are characterized in terms of reduced porosity, average coating thickness and air-flow resistance. Subsequently, the coated and uncoated foams are employed to construct tapered inserts installed at the trailing edge of an NACA 0018 airfoil. The noise mitigation performances of the coated metal foams are compared to those of uncoated metal foams with either similar pore size or permeability value, and both are compared to the solid trailing edge reference case. Results show that that the permeability of the foam can be easily altered by the application of an internal coating on the metallic foams. The noise reduction characteristics of the coated foams are similar to equivalent ones with metallic materials, provided that the coating material is rigid enough not to plastically deform under flow conditions.
对采用孔径为亚毫米级的开孔镍铬铝泡沫制成的多孔后缘进行的研究表明，在减轻湍流边界层后缘噪声方面取得了令人鼓舞的成果。然而，所实现的噪声减轻通常取决于孔隙几何形状，而孔隙几何形状在制造后是固定的。在本研究中，通过在泡沫内部结构上涂覆聚合物涂层，采取了控制这种多孔后缘气动声学效应的措施。使用这种方法，泡沫的内部拓扑结构得以保持，但其渗透率受到显著影响。由于聚合物涂层具有温度响应性，并且其厚度可以在泡沫内部进行控制，因此本研究开启了气动声学控制的新可能性。对孔径为580、800和1200μm的多孔金属泡沫进行（内部）喷涂弹性体涂层。对未涂覆和涂覆的泡沫在孔隙率降低、平均涂层厚度和气流阻力方面进行了表征。随后，使用涂覆和未涂覆的泡沫来构建安装在NACA 0018翼型后缘的锥形插件。将涂覆金属泡沫的噪声减轻性能与具有相似孔径或渗透率值的未涂覆金属泡沫的性能进行比较，并将两者与实心后缘参考案例进行比较。结果表明，通过在金属泡沫上施加内部涂层，可以轻松改变泡沫的渗透率。如果涂层材料足够坚硬，在流动条件下不会发生塑性变形，那么涂覆泡沫的降噪特性与金属材料的等效特性相似。
