Characterization of instability mechanisms on sharp and blunt slender cones at Mach 6
Characterization of instability mechanisms on sharp and blunt slender cones at Mach 6
复制标题
6 马赫数下锐利和钝细锥体不稳定机制的表征
DOI：
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发表时间：
2022
影响因子：
3.7
通讯作者：
S. Laurence
中科院分区：
文献类型：
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作者：
R. E. Kennedy;J. Jewell;P. Paredes;S. Laurence
摘要 进行实验以研究鼻尖钝度对马赫 6 自由流中 $7^{circ }$ 半角锥体上导致边界层转变的不稳定机制的影响。使用高速校准纹影图像和压力测量的组合来表征干扰的发展，并将数据与使用抛物化稳定性方程计算的结果进行比较。大约 414 毫米长的锥形模型配备了可互换的鼻尖，半径范围从尖锐到 5.08 毫米。对于半径为 $R_{N}<2.54 { 的鼻尖
m mm}$，第二模式不稳定波是导致转变的主要机制。根据校准的纹影可视化和压力测量计算出的时间平均频谱用于计算第二模式最大放大频率和积分放大率（$N$ 因子）。在每个自由流条件下，尖头配置的线性增长状态下的测量和计算之间观察到良好的一致性。此外，双谱分析还确定了导致高次谐波增长的频率成分的二次锁相。适用于 $R_{N}geqslant 2.54 { 的鼻尖
m mm}$，纹影可视化区域位于熵层吞噬长度的上游，并且第二模态波在边界层内不再可见；相反，在熵层和边界层边缘之间会形成细长的、陡峭的倾斜特征，这些特征被认为与非模态不稳定机制相关。同时采集的表面压力测量结果揭示了高频压力振荡，类似于与这些非模态特征的后缘相关的第二模式不稳定波。
Abstract Experiments are performed to investigate the effect of nose-tip bluntness on the instability mechanisms leading to boundary-layer transition on a $7^{circ }$ half-angle cone in a Mach-6 free stream. The development of disturbances is characterized using a combination of high-speed calibrated schlieren images and pressure measurements, and the data are compared with results computed using the parabolized stability equations. The approximately 414 mm long cone model is equipped with an interchangeable nose tip ranging from sharp to 5.08 mm in radius. For nose tips with a radius $R_{N}<2.54 {
m mm}$, second-mode instability waves are the dominant mechanism leading to transition. Time-averaged frequency spectra computed from the calibrated schlieren visualizations and pressure measurements are used to compute the second-mode most-amplified frequencies and integrated amplification rates ($N$ factors). Good agreement is observed between the measurements and computations in the linear-growth regime for the sharp-nose configuration at each free-stream condition. Additionally, a bispectral analysis identifies quadratic phase locking of frequency content responsible for the growth of higher harmonics. For nose tips of $R_{N}geqslant 2.54 {
m mm}$, the schlieren visualization region is upstream of the entropy-layer swallowing length, and second-mode waves are no longer visible within the boundary layer; instead, elongated, steeply inclined features believed to be associated with non-modal instability mechanisms develop between the entropy-layer and boundary-layer edges. Simultaneously acquired surface pressure measurements reveal high-frequency pressure oscillations similar to second-mode instability waves associated with the trailing edge of these non-modal features.