Characteristics of wall pressure fluctuations in separated flows over a backward-facing step: Part II. Unsteady wavelet analysis

 Time-dependent characteristics of wall pressure fluctuations in separated and reattaching flows over a backward-facing step were investigated by means of the continuous wavelet transform. Emphasis was placed on the combination of time-localized analyses of the wavelet transform and multi-point measurements of pressure fluctuations. Synchronized wavelet maps revealed the evolutionary behavior of pressure fluctuations and gave further insight into the modulated nature of large-scale vortical structures. It was found that there exist two modes of shed vortices: one is the global oscillation and the other is the vortex convection. The two alternating modes are synchronized with the flapping frequency component of pressure fluctuations. The flapping motion gives rise to the difference in pressure spectra, indicating more intensive pressure activity during the shrinking period of the recirculation region.