High order numerical simulations of underexpanded supersonic cold jets issuing from a circular sonic nozzle are conducted to investigate the effective source location of axisymmetric mode screech tones. The frequency and sound pressure level of screech tone agree well with the experimental results in literature. The detailed generation processes of axisymmetric screech modes in a complete cycle are exhibited through investigating the dynamic evolutions of the flow structures and acoustic waves. By implementing spectral proper orthogonal decomposition (SPOD) of jet velocity field and pressure field, the corresponding SPOD modes to the ${\mathrm{\text{A}}}_1$ and ${\mathrm{\text{A}}}_2$ screech modes are extracted respectively and their evolutions along streamwise direction are analyzed. The source location of ${\mathrm{\text{A}}}_1$ mode and ${\mathrm{\text{A}}}_2$ mode screech tones were revealed based on the dynamic evolution analysis and the Fourier mode decomposition. It is worth noting that the screech waves of each axisymmetric screech mode radiate from an isolated discrete source rather than the distributed sources at a given jet Mach number. Another interesting finding is that the effective source position of screech ${\mathrm{\text{A}}}_2$ mode varies with jet Mach number.

对从圆形音速喷嘴发出的欠膨胀超音速冷射流进行高阶数值模拟，以研究轴对称模式尖叫声的有效源位置。尖叫音的频率和声压级与文献中的实验结果吻合较好。通过研究流动结构和声波的动态演化，展示了轴对称尖叫模式在一个完整循环中的详细生成过程。通过对射流速度场和压力场进行谱本征正交分解（SPOD），得到相应的SPOD模态${\mathrm{\text{A}}}_{\mathrm{1个}}$和${\mathrm{\text{A}}}_{\mathrm{2个}}$分别提取尖叫模态，分析其沿流向的演化过程。的源位置${\mathrm{\text{A}}}_{\mathrm{1个}}$模式和${\mathrm{\text{A}}}_{\mathrm{2个}}$基于动态演化分析和傅里叶模态分解揭示了模态尖叫声。值得注意的是，每个轴对称尖叫模式的尖叫波都是从一个孤立的离散源辐射的，而不是给定喷气马赫数的分布式源。另一个有趣的发现是尖叫声的有效源位置${\mathrm{\text{A}}}_{\mathrm{2个}}$模式随喷气马赫数而变化。