The characteristic behaviors of low-frequency modulations embedded in the vortex shedding process behind a trapezoidal cylinder were studied experimentally. Hot-wire signals and smoke-wire visualization images were acquired simultaneously to examine the correlation between low-frequency modulations and the vortex formation length. Wavelet analysis was performed to extract the instantaneous properties from the raw hot-wire signals measured upstream of the trapezoidal cylinder model. Results show that the variations of instantaneous vortex shedding frequency appear to be in negative correlation with the low-frequency modulations and that the cross-correlation coefficient can reach —0.5. This substantiates that the low-frequency modulations observed are linked with the vortex shedding process.
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