Focused laser differential interferometry measurement of instability wave in a hypersonic boundary-layer
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摘要: 地面风洞实验是开展高超声速边界层转捩研究的主要手段之一，但是目前可用于高超声速边界层三维空间测量的实验技术仍极为缺乏，且已有测量技术的动态响应频率普遍较低。基于光的折射和干涉原理，搭建了一套非介入式聚焦激光差分干涉仪测量系统（Focused Laser Differential Interferometry，FLDI），可有效获取三维流场空间点的密度变化。在马赫数为8的常规高超声速风洞中，使用FLDI开展了来流雷诺数107/m、7°半锥角尖锥标模边界层的不稳定波测量实验。结果显示FLDI成功捕获到频率在327 kHz的第二模态不稳定波及其谐波（645 kHz）。通过与PCB测试结果进行对比，FLDI的高信噪比、高解析频率（本文实验有效解析频率1.5 MHz）、高空间分辨率（沿流向小于1 mm）等优点得以体现。鉴于FLDI的高时空分辨率等优良特性，其可用于高超声速边界层不稳定波行为以及感受性等问题的研究，为深入认识高超声速边界层转捩机制以及感受性问题提供了有效手段。Abstract: The wind tunnel experiment is one of the most important methods to conduct the hypersonic boundary-layer transition research. However, the experimental technology that can be used for three-dimensional hypersonic boundary-layer measurement is still extremely lacking, and the dynamic response of the existing measurement technology is quite restricted. In order to solve the above problems, a non-instrusive Focused Laser Differential Interferometry (FLDI) measurement system is set up based on the light refraction and interference principle and it can effectively measure the density disturbance of the flow field at spatial points. A hypersonic laminar/turbulent boundary-layer transition experiment was carried out on a 7° half angle sharp cone model in a conventional Mach 8 hypersonic wind tunnel with FLDI being the main diagnostic. The results show that FLDI successfully captures the second mode instability wave at 327 kHz and its 645 kHz harmonics. In comparison with PCB test results, FLDI has the advantages of high Signal to Noise Ratio, high dynamic response and high spatial resolution (less than 1 mm along the flow direction). Considering its excellent characteristics such as high spatial and temporal resolution, FLDI can be used as a promising diagnostic for the hypersonic boundary-layer transition and receptivity study.
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图 11 FLDI测得边界层第二模态不稳定波
Figure 11. Second mode instability wave in boundary layer captured by FLDI
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