高度欠膨胀声速射流的自相似特性

构建了高压气体射流模型和高分辨率的计算网格，对喷压比（NPR）为5.60、流动雷诺数Re为105量级的高度欠膨胀射流进行了三维大涡模拟（LES）计算.讨论了时均的射流近场结构，发现大涡模拟成功捕捉到了高度欠膨胀射流近场的典型波系结构，并与文献结果吻合较好.研究着重定量考察流向速度和氮气质量分数的分布规律，以揭示高度欠膨胀射流的自相似特性.结果表明:在射流核心区之后，不同流向位置上流向速度和氮气质量分数沿径向的分布呈现出与亚声速射流类似的自相似特性.但射流流场开始呈现自相似的位置仍然为超声速，这是高度欠膨胀射流自相似特性的独有特征.提出了高斯拟合公式，在靠近和远离射流中心线的区域内均可较好地表征射流的自相似特性.此外，还考察了射流剪切层的发展特征，比较了计算得到的射流剪切层增长率与先前实验测量结果的差异，并分析了其中可能的原因. 

Self-similarity characteristics of highly underexpanded sonic jet

A three-dimensional large eddy simulation(LES) of a highly underexpanded jet with nozzle pressure ratio(NPR) of 5.60 and the magnitude of flow Reynolds number of 105 was carried out based on high-pressure gas jet injection model and high-resolution mesh. The near-field wave structures of the highly underexpanded jet were successfully captured by LES, and also agreed well with the available references data. The quantitative investigation of the radial distributions of streamwise velocity and nitrogen mass fraction was performed to reveal the self-similarity characteristics of the highly underexpanded jet.Result showed that,the self-similarity characteristics of radial profiles of streamwise velocity and nitrogen mass fraction previously observed for subsonic jets were also confirmed in the downstream jet core for the current highly underexpanded jet. The flow where the self-similarity started was still supersonic, showing a distinctive feature for the self-similarity characteristics of highly underexpanded jets. The proposed Gauss fitting formulas can well present the self-similarity characteristics of the regions close to or far away from the jet centerline. In addition, the development feature of the jet shear layer was studied, the jet growth rate obtained was compared with the previous experimental results, and the possible explanation for the difference was observed.