The structure of turbulent wall-bounded flows is comprised by a complete spectrum of scales. Studies showed that the large-scale structures of the outer layer influence near-wall small-scale structures by several mechanisms, namely, superposition, amplitude and frequency modulation, and distortions by sweeps and ejections. Most analyses focus on one specific aspect of these phenomena, which means that the full interaction scenario is not comprehensively analyzed. In this paper, a method is presented which targets the combined effect of superposition, amplitude modulation, and distortions on the near-wall dynamics. It is validated against synthetic signals to provide a reliable tool for further analysis including the scale separation technique and the detection and elimination of large-scale influences. For the sake of clarity, the proposed method is applied to one-dimensional signals. Besides synthetic data, one-dimensional time-dependent streamwise velocity fluctuations of a near-wall and an outer-layer location extracted from a three-dimensional direct numerical simulation of a turbulent channel flow at ${\text{Re}}_{\tau }\approx 1000$ are analyzed. The paper shows that scale separation by the empirical mode decomposition approach and by conventional spectral filtering yields similar conclusions about the interaction mechanisms. However, the empirical mode decomposition is advantageous since it does not require any a priori knowledge about the analyzed flow and, thus, preprocessing and error sources are reduced. Furthermore, an approach for the investigation of the amplitude modulation is presented. Compared to existing techniques, it is superior in revealing this phenomenon due to a preceding removal of the influences of superposition and distortions and a different approach to determine the near-wall modulation. The near-wall and the outer-layer large-scale amplitudes are determined from the analytical large-scale signals, which are obtained by the Hilbert transform. Unlike conventional methods, this approach reveals the existence of a significant amplitude modulation across the channel half-height.

中文翻译：

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检测湍流边界流中的小规模/大规模相互作用

湍流壁流的结构由完整的尺度范围组成。研究表明，外层的大尺度结构通过几种机制影响近壁小尺度结构，即叠加，振幅和频率调制以及扫描和喷射引起的畸变。大多数分析集中于这些现象的一个特定方面，这意味着没有全面分析完整的交互方案。本文提出了一种针对叠加，幅度调制和失真对近壁动力学的综合影响的方法。它已针对合成信号进行了验证，为进一步的分析提供了可靠的工具，包括水垢分离技术以及大范围影响的检测和消除。为清楚起见，该方法适用于一维信号。除了合成数据，还从湍流通道流动的三维直接数值模拟中提取了近壁和外层位置的一维随时间变化的流速度波动。${\text{回覆}}_{\tau }\approx 1000$被分析。本文表明，通过经验模态分解方法和常规光谱过滤进行的水垢分离得出有关相互作用机理的相似结论。然而，经验模态分解是有利的，因为它不需要任何先验减少了有关分析流程的知识，从而减少了预处理和错误源。此外，提出了一种用于调幅的研究方法。与现有技术相比，由于事先消除了叠加和畸变的影响以及确定近壁调制的不同方法，它在揭示此现象方面具有优势。从解析的大规模信号确定近壁和外层的大规模振幅，这些信号是通过希尔伯特变换获得的。与常规方法不同，此方法揭示了整个通道半高处都存在明显的幅度调制。