Unsteady flow characteristics of a normal shock wave, a lambda foot, and a separated turbulent boundary layer are investigated within a unique test section with supersonic inlet flow. The supersonic wind tunnel facility, containing this test section, provides a Mach number of approximately 1.54 at the test section entrance. Digitized shadowgraph flow visualization data are employed to visualize shock wave structure within the test section. These data are analyzed to determine shock wave unsteadiness characteristics, including grayscale spectral energy variations with frequency, as well as time and space correlations, which give coherence and time lag properties associated with perturbations associated with different flow regions. Results illustrate the complexity and unsteadiness of shock-wave-boundary-layer-interactions, including event frequencies from grayscale spectral energy distributions determined using a Lagrangian approach applied to shock wave location, and by grayscale spectral energy distributions determined using ensemble-averaging applied to multiple closely-located stationary pixel locations. Auto-correlation function results and two-point correlation functions (in the form of magnitude squared coherence) quantify the time-scales of periodic events, as well as the coherence of flow perturbations associated with different locations, over a range of frequencies. Associated time lag data provide information on the originating location of perturbation events, as well as the propagation direction and event sequence associated with different flow locations. Additional insight into spatial variations of time lag and flow coherence is provided by application of magnitude squared coherence analysis to multiple locations, relative to a single location associated with the normal shock wave.

中文翻译：

---

利用空间和时间相关性分析冲击波的不稳定性，并将其应用于阴影图流可视化数据

在具有超音速进气流的独特测试区内，研究了正常冲击波，λ足和分离的湍流边界层的非稳态流动特性。包含该测试区的超音速风洞设施在测试区入口处提供的马赫数约为1.54。数字化的阴影图流量可视化数据用于可视化测试部分内的冲击波结构。分析这些数据以确定冲击波的不稳定特性，包括灰度频谱能量随频率的变化以及时间和空间的相关性，从而提供与不同流动区域相关的扰动相关的相干性和时滞特性。结果说明了冲击波边界层相互作用的复杂性和不稳定性，包括事件频率，这些事件频率来自使用拉格朗日方法确定的灰度光谱能量分布应用于冲击波位置，以及通过使用集合平均确定的灰度光谱能量分布应用于多个紧密定位的固定像素位置。自相关函数结果和两点相关函数（以幅度平方相干的形式）在一定频率范围内量化了周期性事件的时间尺度以及与不同位置相关的流扰动的相干性。关联的时滞数据提供有关扰动事件的始发位置以及与不同流位置关联的传播方向和事件序列的信息。