Hilbert and Wavelet Analyses of Unsteady, three-dimensional Characteristics of Vortex Shedding from a Circular Cylinder

運用Hilbert和Wavelet轉換分析圓柱渦流溢放三維非定常特性

苗君易(J. J. Miau) ； 杜榮國(C. C. Hu) ； 胡志忠(J. K. Tu)

《中國機械工程學刊》 28卷1期 (2007/02) Pp. 99-109

https://doi.org/10.29979/JCSME.200702.0012

摘要

本文利用Hilbert和Wavelet轉換分析與比較MEMS感測器在圓柱表面所量測的訊號，實驗是在雷諾數10^4情況下進行。由分析MEMS信號發現，Hilbert分析法結果可明顯地指出渦流位錯現象會發生的位置，可能在圓柱表面上某些區域或整個圓柱，其時間尺度長達數個渦流溢放週期。比較Hilbert分析法和小波(Wavelet)分析法結果發現可得到一致的渦流溢放相變化。然而，小波分析法結果隨時間的變化較Hilbert分析法結果為平滑，此乃因小波分析法本身具有濾波之功能。

並列摘要

The techniques of Hilbert and Wavelet transformations were applied to analyze the signals of the MEMS sensors situated on a circular cylinder spanwisely for examining the unsteady, three-dimensional behavior of vortex shedding. The experiments were made at Reynolds numbers of 10^4. The results of the Hilbert analysis show that the unsteady, three-dimensional characteristics of vortex shedding are highlighted by the events of vortex dislocation, which might be occurred in a localized spanwise region or over the entire cylinder for a time length up to several vortex shedding periods. The temporal variations of spanwise phase difference of vortex shedding reduced by the Hilbert analysis were noticed in good agreement with those obtained by the Wavelet analysis. On the other hand, it is noted that the temporal variations of Wavelet analysis appear more smoothened than those of the Hilbert analysis. This is attributed to the nature of windowed smoothing of the Wavelet transformation.

並列關鍵字

Hilbert transformation ； Wavelet transformation ； vortex dislocation