Abstract A lattice-Boltzmann method has been employed to study the aeroacoustics and aerodynamics of airfoils equipped with leading edge treatments, namely the porous leading edge and leading edge serrations. The present study aims to identify the differences in noise reduction mechanisms between the two treatments. Within the context of turbomachinery applications, the airfoils undergo aerodynamic excitation due to the impingement of turbulent wake shed by an upstream rod. Two airfoil profiles are considered: NACA 0012 and NACA 5406; the latter mimics geometrical features and aerodynamic loading distribution of the outlet-guide vane in a turbofan test rig. Simulations are carried out at a freestream Mach number of 0.22, corresponding to Reynolds number based on the rod diameter of 48 000. The serrations are designed to follow a sinusoidal planform shape, whereas the porous leading edge is based on a Ni-Cr-Al metal-foam with homogeneous and isotropic properties. It is found that the porous leading edge attenuates noise by dampening surface pressure fluctuations due to the reduced blockage effect compared to the solid one. Differently, the leading edge serrations promote destructive interference of noise sources along the span. When applied against turbulent inflow with tonal characteristic, such as that induced by the impingement of Karman vortex street in the rod wake, the latter is more effective. On the other hand, both treatments are found to produce similar broadband noise reduction. When comparing aerodynamic performances, it is found that under a lifting condition, cross-flow is present through the porous material which results in lift reduction and drag increase. A serrated porous leading edge is then proposed to combine the benefits of the two leading edge treatments. This results in optimal noise reduction performances and lower aerodynamic penalty with respect to the fully porous leading edge.

中文翻译：

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使用多孔材料和锯齿的杆翼型结构前缘降噪数值研究

摘要 采用格子-玻尔兹曼方法研究了带有前缘处理的翼型，即多孔前缘和前缘锯齿的气动声学和空气动力学。本研究旨在确定两种处理方法之间降噪机制的差异。在涡轮机械应用的背景下，由于上游杆释放的湍流尾流的冲击，翼型经历空气动力学激发。考虑了两种翼型：NACA 0012 和 NACA 5406；后者模仿涡轮风扇试验台中出口导向叶片的几何特征和空气动力学载荷分布。模拟是在 0.22 的自由流马赫数下进行的，对应于基于 48 000 杆直径的雷诺数。锯齿设计为遵循正弦平面形状，而多孔前缘基于具有均匀和各向同性特性的 Ni-Cr-Al 金属泡沫。发现多孔前缘通过抑制表面压力波动来衰减噪音，这是由于与实心相比减少了阻塞效应。不同的是，前缘锯齿会促进噪声源沿跨度的破坏性干扰。当应用于具有音调特征的湍流流入时，例如由卡门涡街在杆尾流中的撞击引起的湍流，后者更有效。另一方面，发现两种处理都产生类似的宽带降噪。在比较气动性能时发现，在升力条件下，通过多孔材料存在错流，导致升力降低和阻力增加。然后提出锯齿状多孔前缘以结合两种前缘处理的优点。相对于完全多孔的前缘，这导致最佳的降噪性能和更低的空气动力学损失。