Linear modes in a planar turbulent jet
Linear modes in a planar turbulent jet
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平面湍流射流中的线性模式
DOI：
10.1017/jfm.2020.25
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Antonio Segalini
中科院分区：
文献类型：
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作者：
Masaharu Matsubara;P. Henrik Alfredsson;Antonio Segalini
研究了从完全发展的二维湍流通道流中发出的平面射流，重点是射流核心的横向扑动。使用 X 型探头通过热线风速测定法测量流向和横向速度。首先表征平均速度场和速度协方差以评估未受干扰的流场。从安装在通道出口处的槽引入周期性激励，并通过使用锁相平均技术获得信号的相干波动部分，其中周期性初始强迫用作触发。这使得能够导出与引入的扰动相关的相干结构。发现其幅度与初始强迫强度成正比，并且在初始强迫幅度一定范围内，增长曲线以及提取的波动的空间分布是相同的。并行和非并行线性稳定性理论定性和定量地捕获了所导出的相干结构的特征。湍流射流中线性模式的存在意味着在自然（非受迫）射流中观察到的大规模扰动可以被视为一组不相干的线性模式。
A planar jet issuing from a fully developed two-dimensional turbulent channel flow is studied, with a focus on the transverse flapping of the jet core. The streamwise and transverse velocities were measured with hot-wire anemometry using an X-type probe. The mean velocity field and the velocity covariances were first characterised to assess the undisturbed flow field. Periodic excitations were introduced from a slot mounted at the channel exit and the coherent fluctuating part of the signal was obtained by using a phase-locked averaging technique, where the periodic initial forcing was used as trigger. This enabled the eduction of the coherent structure associated with the introduced perturbation. Its amplitude was found to be directly proportional to the intensity of the initial forcing and, within a certain range of the initial forcing amplitude, the growth curves were identical as well as the spatial distribution of the extracted fluctuations. Parallel and non-parallel linear stability theory captures qualitatively and quantitatively the features of the educed coherent structure. The existence of the linear mode in the turbulent jet implies that the large-scale perturbations observed in natural (unforced) jets can be regarded as an incoherent set of linear modes.