AI 中文总结
通过DSMC方法分析不同KnD下的高超声速氮气绕圆柱流动，解析出弓形激波层中弱慢集体位移，该位移为嵌入宽带波动的低通响应，密度层拓宽82%时角形状仍高度一致。
AI 中文摘要
采用时间分辨的直接模拟蒙特卡洛（DSMC）流场，研究分离型稀薄高超声速弓形激波是否包含可与相关粒子采样波动分离的慢集体位移。分析马赫数10、转动弛豫的氮气绕圆柱流动，其基于直径的克努森数范围为0.01≤KnD≤1，其中KnD=λ∞/D，λ∞为来流平均自由程，D为圆柱直径。在垂直于壁面的射线上提取密度半跃前沿，排除无支撑的固体侧点，在特征提取前进行时间粗粒化处理。使用惩罚复合拟合得分、设计尺度交叉验证、块重采样、合成控制及互补全场匹配滤波器，比较持久分量与采样协方差分量。校正后的场本征正交分解（POD）在所有克努森数下均为高阶，却在KnD=0.01和0.025时解析出弱的同号角位移。独立的随机种子和模拟器粒子加载重复实验可恢复角形状与弛豫时间，而原始采样方差随加载变化。在两个解析状态中，平均密度层拓宽82%，而角形状保持高度一致。密度和压力对标记运动的恢复最强；KnD=0.025时约化马赫数和平动温度的参与度，是与矩选择性弱化一致的证据，尽管依赖可观测量的信噪比仍可能是影响因素。该信号被解释为嵌入宽带动力学波动中的低通弓形层响应，而非新发现的离散振荡或已证实的线性不稳定性。较高克努森数的记录灵敏度不足，无法确定其物理消失。
英文摘要
Time-resolved direct simulation Monte Carlo (DSMC) fields are used to test whether a detached rarefied hypersonic bow shock contains a slow collective displacement that can be separated from correlated particle-sampling fluctuations. Mach-10 rotationally relaxing nitrogen flow over a circular cylinder is analysed for diameter-based Knudsen number $0.01\leq \KnD\leq1$, where $\KnD=λ_\infty/D$, $λ_\infty$ is the freestream mean free path and $D$ is the cylinder diameter. A density half-jump front is extracted on body-normal rays, unsupported solid-side points are excluded, and temporal coarse graining is performed before feature extraction. Persistent and sampling covariance components are compared using a penalized composite-fit score, design-scale cross-validation, block resampling, synthetic controls and complementary full-field matched filters. Corrected field proper orthogonal decomposition (POD) is high rank at every Knudsen number, yet a weak, same-signed angular displacement is resolved at $\KnD=0.01$ and $0.025$. Independent random-seed and simulator-particle-loading repeats recover the angular shape and relaxation time while the raw sampling variance changes with loading. Across the two resolved states the mean density layer broadens by $82\%$, while the angular shapes remain strongly aligned. Density and pressure recover the marker motion most strongly; the reduced Mach-number and translational-temperature participation at $\KnD=0.025$ is evidence consistent with moment-selective weakening, although observable-dependent signal-to-noise remains a possible contributor. The signal is interpreted as a low-pass bow-layer response embedded in broadband kinetic fluctuations, not as a newly discovered discrete oscillation or a demonstrated linear instability. The higher-Knudsen records are not sufficiently sensitive to establish physical disappearance.
