Abstract

Present work aims to insight the influence of bedform transport on velocity power spectra of acoustic Doppler Velocimeter (ADV) in order to address different spectral sub-regimes. Laboratory experiments were conducted over two types of rough bed (d₅₀ = 4 mm): (a) immobile rough bed and (b) mobile bedform. The near-bed spectral characteristics during bedform transport are compared with those in immobile rough bed. An ADV probe, named Vectrino⁺, manufactured by Nortek with acoustic frequency of 10 MHz was used to measure the velocity fluctuations in flows. Instrument noise and high-frequency fluctuation results furious spikes in the velocity signals and therefore, filtration of contaminated data was very much essential to obtain clear velocity power spectra. In this study the acceleration threshold method was applied successfully for filtering the data sets and the velocity power spectra of filtered data set are found to be well fitted the Kolmogorov “–5/3 scaling-law” in the inertial sub-range. Importantly, the spectral sub-regime at low frequencies with a spectral slope of about −1.0 occurred owing to the fact of bedforms development. The results of Taylor microscale and Kolmogorov scale reveal an amplification of eddy sizes in the near-bed flow region attributed to bedform transport and the drastic reduction in pressure energy diffusion in budget analysis implied gain in near-bed turbulence production.

中文翻译：

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床形对粗糙移动床中声多普勒测速数据速度功率谱的响应

摘要

当前的工作旨在了解床形运输对声学多普勒测速仪（ADV）的速度功率谱的影响，以解决不同的频谱子领域。在两种类型的粗糙床（d ₅₀ = 4 mm）上进行了实验室实验：（a）不动的粗糙床和（b）移动的床形。将床形运输过程中的近床光谱特性与固定式粗糙床中的近床光谱特性进行了比较。一个名为Vectrino ⁺的ADV探针由Nortek制造的声学频率为10 MHz的传感器用于测量流速的波动。仪器噪声和高频波动会导致速度信号中出现尖峰，因此，对污染数据进行过滤对于获得清晰的速度功率谱非常重要。在这项研究中，成功​​使用了加速度阈值方法对数据集进行了滤波，并且发现滤波后的数据集的速度功率谱非常适合惯性子范围中的Kolmogorov“ –5/3比例定律”。重要的是，由于床形的发展，出现了频谱斜率约为-1.0的低频子谱。