Abstract

In this work, an enhanced version of the focused laser differential interferometer (FLDI) is used to measure second-mode instabilities in the boundary layer on a flared cone in Mach 6 quiet flow. A diffractive optical element added to the FLDI system provides six beams that pass through a single Wollaston prism, allowing for multiple points of measurements without the need for additional Wollaston prisms. This technique, linear array-FLDI (LA-FLDI), is used for six simultaneous measurements of second-mode instabilities in a hypersonic boundary layer. This is the first time that this variation of FLDI has been used for second-mode instability measurements and demonstrates that the inclusion of a diffractive optical element into the traditional FLDI and splitting of beam power does not preclude such usage. Thus, LA-FLDI appears to have significant potential for increasing the efficiency of measurements of high-speed boundary layers by enabling multiple measurements at different locations within a single facility run. The velocity of the second-mode wavepacket is estimated and a bispectral analysis is presented showing that harmonics are associated with quadratically phased coupled interactions.

Graphic abstract

中文翻译：

---

线性阵列聚焦激光微分干涉技术检测6马赫静流中喇叭形锥面的第二模不稳定性

摘要

在这项工作中，使用聚焦增强型激光差分干涉仪（FLDI）的增强版来测量6马赫静流中扩口锥的边界层中的第二模式不稳定性。添加到FLDI系统的衍射光学元件可提供六束光束，这些光束穿过单个Wollaston棱镜，从而无需额外的Wollaston棱镜即可进行多个测量点。这种技术，即线性阵列-FLDI（LA-FLDI），用于在超音速边界层中同时测量第二种模式的不稳定性。这是首次将FLDI的这种变化用于第二模式不稳定性测量，并证明了将衍射光学元件包含在传统FLDI中以及光束功率的分离并不排除这种用法。因此，通过在单个设施运行中的不同位置进行多次测量，LA-FLDI似乎具有提高高速边界层测量效率的巨大潜力。估计了第二模波包的速度，并进行了双谱分析，表明谐波与二次相耦合相互作用有关。

图形摘要