Abstract
We demonstrate that free-stream turbulence has a strong impact on the dynamics of flow past a cylindrical roughness element. Previous works have shown that, depending on operating conditions, the leading flow instability can either be varicose (symmetric) or sinuous (antisymmetric). In both cases, when the flow is excited by broadband frequency forcing, dynamic mode decomposition extracts only varicose coherent structures, even though optimal response analysis predicts strong amplification of sinuous disturbances with frequency near the marginally stable sinuous eigenmode. We show that this is due to the flow essentially being an amplifier of varicose perturbations rather than a resonator.
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