Mode Decomposition Analysis Applied to Study the Low-Frequency Embedded in the Vortex Shedding Process

A new method of the mode decomposition method developed by Huang et al. (1998) was applied to decompose the raw signal into a range of fluctuating components from high to low-frequencies in the study. Experimental results of base pressure signals were obtained at Re = 11760 and 31600, respectively. Results show that decomposition method is useful for further studying the low-frequency variations and other fluctuating components in rang of high to low frequencies structures. At the flow condition of Re = 11760, the vortex-shedding structures were exactly referred to the mode C2 and the residue component of R5 mainly contained the component of the low-frequency variations. Similarly, results obtained at Re = 31600 show that the vortex-shedding structure can be identified with the mode C1 and the residue component of R4 also contained a substantial component of low frequency variations. These results show that all the flow structures could be exactly decomposed into intrinsic oscillatory modes of flow structure and residue components of other flow structure by this technique. Here, the low-frequency variations naturally belong to the residue component but not the mono flow structure. That is to say, the appearance of low-frequency variations embedded in the vortex shedding process would be induced during the modulation process of energy transmission between all the mono flow structures.