多孔介质对圆柱-翼型干涉噪声的影响

采用LES（large eddy simulation）+FW-H（Ffowcs Williams-Hawkings）方程，研究了圆柱表面使用不同PPI（pore number per inch）和厚度的多孔介质对圆柱尾迹及圆柱-翼型干涉噪声的影响，探索了多孔介质的降噪规律和机理。结果表明：多孔介质能稳定圆柱表面的剪切层，抑制旋涡脱落，从而削弱尾迹对下游翼型的影响，圆柱单音噪声最大可降79 dB，翼型单音峰值降低13.22 dB，宽频噪声降低20 dB；多孔材料PPI的变化对降噪效果影响较小，而厚度是影响流场模态、降噪效果及气动性能的一个关键参数；多孔材料厚度合适时，圆柱-翼型流场形态为“剪切层模态”，可有效降低湍流干涉噪声；多孔材料厚度较小时，发现了一种流场形态，即“剪切层-尾迹模态”，导致翼型噪声增大；合适的多孔介质厚度不仅降噪效果显著，对圆柱-翼型的气动性能也有改善作用。     

Far-field sonic boom prediction considering atmospheric turbulence effects: An improved approach

Accurate prediction of sonic boom is one of key challenges for the design of a low-boom supersonic aircraft. For most of available far-field prediction methods, the effect of atmospheric turbulence appearing in the planetary boundary layer cannot be considered, which results in remarkable inaccuracy of predicting ground-level sonic boom waveform. Although some efforts have been made to overcome the shortcoming, the turbulence effects are not yet well described so far. This article proposes an improved method by extending the two-dimensional Heterogeneous One-Way Approximation for the Resolution of Diffraction (HOWARD) equation to account for the axial and transverse convections of wind fluctuation as well as the effect of temperature fluctuation. The proposed method is validated by comparing the predictions with the flight-test data of JAXA D-SEND#1 LBM, which shows that the result of the proposed method is in better agreement with the flight-test data than that of the method without considering atmospheric turbulence effects. Then, distortion mechanism of sonic boom waveforms caused by atmospheric turbulence is analyzed by using the proposed method. It is indicated that the effect of turbulent convection makes uniform sonic-boom wavefronts irregular, which creates the condition of diffraction effect to perturb waveforms. Finally, the proposed method is applied to investigate the behavior of two types of waveforms given by the sonic boom minimization theory. Results show that a far-field waveform with a weaker initial shock is more beneficial for low-boom design of a supersonic aircraft.