Power-Spectral density estimate of the Bloor-Gerrard instability in flows around circular cylinders
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There have been differences in the literature concerning the power law relationship between the Bloor-Gerrard instability frequency of the separated shear layer from the circular cylinder, the Bénard-von Kármán vortex shedding frequency and the Reynolds number. Most previous experiments have shown a significant degree of scatter in the measurement of the development of the shear layer vortices. Shear layers are known to be sensitive to external influences, which can provide a by-pass transition to saturated growth, thereby camouflaging the fastest growing linear modes. Here, the spatial amplification rates of the shear layer instabilities are calculated using power-spectral density estimates, allowing the fastest growing modes rather than necessarily the largest structures to be determined. This method is found to be robust in determining the fastest growing modes, producing results consistent with the low scatter results of previous experiments.
KeywordsWind Tunnel Shear Layer Circular Cylinder Instability Wave Momentum Thickness
We are greatly indebted to Martin Welsh for providing the experimental facilities at the CSIRO. Moses Khor acknowledges the support of a Monash Graduate Scholarship. This research was supported under Australian Research Council’s Large Grant Projects funding scheme A89131241.
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