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Wake dynamics of surface-mounted obstacles in highly pulsatile flow Open Access

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Flow pulsatility is ubiquitous in biological and biomedical fluid dynamics. Among the most fruitful means of studying these complex, biological systems is through the use of simplified models exposed to basic parameter changes. This approach is employed herein on a relatively unstudied, canonical flow configuration. Using experiments and simulations, we examine highly pulsatile flow over surface-mounted bluff bodies, observe the wake dynamics, and investigate several important aspects of this large parameter space. As the first step in documenting this unstudied flow configuration, i.e. surface-mounted obstacles and pulsatile flow, a surface-mounted hemisphere is exposed to a highly pulsatile freestream flow, the phase-averaged wake dynamics are documented revealing an arch vortex in the near wake, and an explanation of the arch vortex's dynamics based on self-induced vortex propagation is proposed and quantitatively supported. The next set of experiments is focused on the effects of obstacle geometry. A low aspect ratio, surface-mounted, circular cylinder and cube are exposed to a similar highly pulsatile freestream flow revealing the robustness and lack of geometry dependence of the arch vortex propagation phenomena reported for the hemisphere. Next, a set of validated direct numerical simulations, revealed the arch vortex forms with each accelerating inflow phase, is coherent in an instantaneous sense, and is a starting vortex akin to those shed from impulsively start airfoils. Lastly, the effects of varying the frequency of freestream inflow pulsation on the wake dynamics are reported. Ranging from low-frequency, quasi-steady case to high-frequency pulsation, the effects of pulsation frequency were documented experimentally and numerically. A regime map of the wake dynamics with changing frequency is proposed and supported with energy spectral density of pressure measurements. A non-dimensional parameter relevant to all external pulsatile flows is proposed, revealing remarkable similarity to a parameter used in the study of vortex rings.

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