中文摘要：

采用大涡模拟研究了高亚音速、基于直径Reynolds（雷诺）数为Re=10^5的圆喷管构型射流和6齿喷管与4齿喷管构型的锯齿射流．将圆射流的计算结果与前人已有的实验和大涡模拟结果进行了对比，验证了当前计算结果的可靠性．对比研究了锯齿射流与圆射流特征，结果显示锯齿射流在近喷口附近具有更大的径向扩张率和更短的势核区长度：锯齿射流的总声压级在低辐射角度上相比于圆射流可低4dB，而在侧边辐射方向噪声没有明显升高．分析了锯齿射流和圆射流远场压力脉动的前三阶周向Fourier（傅里叶）模态m=0，1，2，结果显示三组算例在同一周向模态上呈现出相似的声压级分布．然而4齿锯齿射流的第零阶和第一阶周向模态在高辐射角度上相较于圆射流具有更高的噪声水平．将POD分解技术用于提取特定周向模态上的最具能量的大尺度结构，在与大尺度结构相关的波包特征角度部分解释了锯齿射流和圆射流远场噪声特性的不同．

英文摘要：

Large eddy simulation （LES） is performed to study high subsonic round and chevron jets with a diameter-based Reynolds number Re = 105. 2 different chevron jet flows are consid- ered, which are with 6 lobes and 4 lobes respectively. The simulation results are checked by comparing mean axial velocity profiles and overall sound pressure levels （ OASPLs ） of the round jet with the existent experimental and LES results, and they are in good agreement with each other. Then the properties of chevron jets are compared with those of round jets. The chevron jets show higher radial expansion rate in the near-nozzle region and shorter potential core lengths. The OASPLs of the chevron jets decrease as high as 4 dB at the shallow angles compared with the round jets and without apparent noise increment at the sideline. 3 azimuthal modes, m - 0,1,2 of the far-field pressure fluctuations from both the round and chevron jets are investigated. All cases show similar OASPL distribution profiles vs. the polar angles for each azimuthal mode. But, apparent noise increment is found at high polar angles in the zeroth and first azimuthal modes for the chevron jet with 4 lobes when compared with the round jet. By performing proper orthogonal decomposition （POD）, the most energetic coherent structures at specified coupled azimuthal wavenumbers are extracted. The wavepacket features associated with coherent structures of round and chevron jets are analyzed in detail to explain changes of noise properties in the far fields.