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Dynamic mode decomposition for estimating vortices and lee waves in a stratified wake

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Abstract

Dynamic mode decomposition (DMD) is an analysis technique for extracting flow patterns and their dynamics from experimental or simulated velocity fields. Here, DMD is applied to experimental data in the vertical center-plane of wakes generated by a towed grid in a stably stratified background, at varying values of the dimensionless Froude and Reynolds Number. The primary goal was to identify dynamically important patterns and reveal the influence of stratification on their initiation and evolution. It is demonstrated that DMD captures lee wave and vortical modes with different length scales successfully. Further, one can construct a mode energy spectrum which shows a clear dependence on Froude Number, with energy transfer to larger scales in the near wake, as the initial shear-triggered Kelvin–Helmholtz roll-ups diffuse and pair with neighbors. Finally, this paper serves as a detailed example of the application of DMD to time-resolved particle imaging velocimetry data for a stratified flow. The results confirm its utility in objective identification of dynamics at different scales of complex fluid flows.

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Acknowledgements

We most gratefully acknowledge the support of ONR Contract N00014-14-1-0422, under the management of Dr. R. Joslin. Kevin K. Chen was supported by the Viterbi Postdoctoral Fellowship through the Viterbi School of Engineering at the University of Southern California.

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Authors and Affiliations

  1. University of Southern California, Los Angeles, CA, 90089, USA

    Xinjiang Xiang & Geoffrey R. Spedding

  2. Institute for Defense Analysis, Center for Communication Research-La Jolla, San Diego, CA, 92121, USA

    Kevin K. Chen

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  1. Xinjiang Xiang
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  2. Kevin K. Chen
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  3. Geoffrey R. Spedding
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Correspondence to Xinjiang Xiang.

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Xiang, X., Chen, K.K. & Spedding, G.R. Dynamic mode decomposition for estimating vortices and lee waves in a stratified wake. Exp Fluids 58, 56 (2017). https://doi.org/10.1007/s00348-017-2344-8

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