This paper investigates the application of flow-permeable materials as a solution for reducing jet-installation noise. Experiments are carried out with a flat plate placed in the near field of a single-stream subsonic jet. The flat plate is modular and the solid surface near the trailing edge can be replaced with different flow-permeable inserts, such as a metal foam and a perforated plate structure. The time-averaged jet flow field is characterized through planar PIV measurements at three different velocities ($M_a=0.3,$ $M_a=0.5$ and $M_a=0.8,$ where $M_a$ is the acoustic Mach number), whereas the acoustic far-field is measured with a microphone arc-array. Acoustic measurements confirm that installation effects cause significant noise increase, up to 17 dB for the lowest jet velocity, particularly at low and mid frequencies (i.e. $St<0.7,$ with the Strouhal number based on the jet diameter and velocity), and mostly in the upstream direction of the jet. By replacing the solid trailing edge with the metal foam, noise abatement of up to 9 dB is achieved at the spectral peak for $M_a=0.3$ and a polar angle $\theta ={40}^{\circ },$ with an overall reduction in the entire frequency range where jet-installation noise is dominant. The perforated plate provides lower noise reduction than the metal foam (7 dB at the spectral peak for $M_a=0.3$ and $\theta ={40}^{\circ }$), and it is less effective at low frequencies. This is related to the values of permeability and form coefficient of the materials, which are the major parameters controlling the pressure balance across the trailing edge and, consequently, the noise generated by the plate. However, despite having a high permeability, the plate with the metal-foam trailing edge still has a distinct noise production at mid frequencies ($St\approx 0.43$ for $M_a=0.3$). Based on the analyses of different treated surface lengths, it is conjectured that the solid-permeable junction in the plate acts as a new scattering region, and thus its position also affects the far-field noise, which is in line with analytical predictions in the literature. Nonetheless, both types of inserts provide significant noise reduction and are potential solutions for the problem of jet-installation noise.

本文研究了可渗透流动的材料作为降低喷射装置噪音的解决方案的应用。实验是通过将平板放置在单流亚音速喷射器的近场中进行的。平板是模块化的，后缘附近的固体表面可以用不同的可渗透流量的插入物代替，例如金属泡沫和多孔板结构。时间平均射流场通过在三个不同速度下的平面PIV测量来表征（${\mathrm{中号}}_{\mathrm{一个}}=0.3，$ ${\mathrm{中号}}_{\mathrm{一个}}=0.5$ 和 ${\mathrm{中号}}_{\mathrm{一个}}=0.8，$ 哪里 ${\mathrm{中号}}_{\mathrm{一个}}$是声学马赫数），而声学远场是通过麦克风弧形阵列测量的。声学测量结果表明，安装效果会导致噪声显着增加，对于最低的射流速度，尤其是在低频和中频时（例如，$\mathrm{小号}Ť<0.7，$的Strouhal数取决于射流的直径和速度），并且大部分在射流的上游方向。通过用金属泡沫代替固体后缘，可在频谱峰值处实现高达9 dB的降噪${\mathrm{中号}}_{\mathrm{一个}}=0.3$ 和极角 $\theta ={40}^{\circ }，$在整个频率范围内总体降低，而喷气发动机的安装噪音占主导。穿孔板提供的降噪效果比金属泡沫低（在频谱峰值处为7 dB，对于${\mathrm{中号}}_{\mathrm{一个}}=0.3$ 和 $\theta ={40}^{\circ }$），并且在低频时效果较差。这与材料的渗透率和形状系数的值有关，这是控制整个后缘压力平衡的主要参数，从而控制板产生的噪音。但是，尽管具有高磁导率，但具有金属泡沫后缘的板在中频处仍会产生明显的噪声（$\mathrm{小号}Ť\approx 0.43$ 对于 ${\mathrm{中号}}_{\mathrm{一个}}=0.3$）。根据对不同处理过的表面长度的分析，推测板中的固-渗结是一个新的散射区域，因此其位置也会影响远场噪声，这与分析中的预测相符。文学。尽管如此，两种类型的插入件都可以显着降低噪音，并且是解决喷气安装噪音问题的潜在解决方案。