An experimental fluctuation analysis is usually conducted via thermal anemometry with hot-wires. However, in the vicinity of oscillating shock waves, this kind of sensor can be destroyed due to strong mechanical loads. On the basis of a sufficient modelling, a wedge-shaped hot-film can be suitable for a quantitative fluctuation analysis across a shock wave. Within this study, the modal analysis according to Kovásznay and Morkovin was adapted from hot-wires to the used wedge hot-film. Additionally, 3-dimensional fluctuation diagrams were derived for the separate as well as for mixed modes. The freestream fluctuations were detected across an oblique shock wave with a wedge hot-film in a constant-temperature mode. The shock was caused by a ramp with a 10° ramp angle placed in a flow with a Mach number of M = 2.5 and a unit Reynolds number of Re_unit = 4.96·10⁶·m⁻¹. The recorded perturbations were decomposed according to the modal analysis and found to be dominated by the acoustic mode. The fluctuations’ amplification across the shock wave and the subsequent decay could clearly be detected. They are in good agreement with the literature.

中文翻译：

---

楔形热膜模态分析对斜向冲击波自由流扰动的实验研究

通常通过热线通过热风速测定法进行实验波动分析。但是，在振荡的冲击波附近，这种传感器可能会由于强大的机械负载而损坏。在充分建模的基础上，楔形热膜可能适用于整个冲击波的定量波动分析。在这项研究中，根据Kovásznay和Morkovin进行的模态分析已从热线应用于二手楔形热膜。此外，还为分离模式和混合模式导出了3维波动图。在恒定模式下，用楔形热膜在斜向冲击波上检测到自由流波动。冲击是由放置在Mach数为M = 2.5，单位雷诺数为Re的流中的倾斜角度为10°的斜坡引起的_单位＝ 4.96·10 ⁶ ·m ^-1。根据模态分析将记录的扰动分解，并发现其以声学模式为主。可以清楚地检测到整个冲击波的波动放大以及随后的衰减。它们与文献非常吻合。