In this work we propose replacing the conventional flat-surface airframe that shields the engine by a wavy surface. The basic principle is to design a wavy pattern to reflect the incoming near-field flow and acoustic perturbations into waves of a particular dominant frequency. The reflected waves will then excite the corresponding frequency of the large-scale structure in the initial region of the jet’s shear layer. By designing the frequency of the reflected waves to be the harmonic of the fundamental frequency that corresponds to the radiated peak noise, the two frequency-modes interact nonlinearly. With the appropriate phase difference, the harmonic dampens the fundamental as it extracts energy from it to amplify. The outcome is a reduction in the peak noise. To evaluate this concept, we conducted Detached Eddy Simulations for a rectangular supersonic jet with and without the wavy shield and verified our numerical results with experimental data for a free jet, as well as, for a jet with an adjacent flat surface. Results show that the proposed wavy surface reduces the jet noise as compared to that of the corresponding flat surface by as much as 4 dB.

在这项工作中，我们建议用波浪形表面替换传统的平面机身，该机身将发动机罩屏蔽。基本原理是设计一种波浪形图案，以将传入的近场流和声扰动反映为特定主导频率的波。然后，反射波将激发射流剪切层初始区域中大型结构的相应频率。通过将反射波的频率设计为与辐射峰值噪声相对应的基本频率的谐波，这两个频率模式将非线性交互。通过适当的相位差，谐波可以抑制基频，因为它会从基频中提取能量进行放大。结果是降低了峰值噪声。为了评估这个概念，我们对带有和不带有波浪形护罩的矩形超音速喷气机进行了分离涡流模拟，并用自由喷气机以及具有相邻平坦表面的喷气机的实验数据验证了我们的数值结果。结果表明，与相应的平坦表面相比，拟议的波浪形表面可将喷射噪声降低多达4 dB。