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Significance Statement
Fluid flow around an obstacle on a wall occurs in many engineering applications and natural settings, e.g. from coral on the ocean floor to wind around tall buildings. Meanwhile, pulsatile flow (fluid flow which pulses like a beating heart) is common in biology, geophysics, and biomedical engineering, as well as other fields. Despite the ubiquity of both, the combination of both, i.e. pulsatile flow over a wall‐mounted obstacle has not been widely studied. Our ongoing study aims to fill this gap in the knowledge base and provide a basis for understanding the complex, and at times unintuitive, fluid dynamics of complex, three‐dimensional, unsteady fluid flow.
The main results of the present study pertain to the vortex dynamics in the wake of a wall-mounted hemisphere. All results presented here were obtained experimentally in a low‐speed wind tunnel. The figure consists of the inflow profile (top), followed by contours of swirling strength concentration (which indicates the location of a vortex)(middle), and a schematic representation of those vortical structures (bottom). The inflow velocity profile can be split into two sections: the acceleration portion and the deceleration portion. The fluid dynamics in the wake of the hemisphere can be split in a similar way.
During acceleration, the freestream flow is the dominant force controlling the vertical dynamics in this flow. During deceleration, the freestream flow loses that dominance and the velocity field of the arch vortex takes over. During this time it moves upstream opposite to the freestream flow in the downstream direction. Vortex dynamics of this kind have not before been characterized. We are now investigating other regions of the wide parameter space in pulsatile, unsteady, external flow.
Journal Reference
Experiments in Fluids, 2016, 57:9.
Ian A. Carr1, Michael W. Plesniak2
[expand title=”Show Affiliations”]- Biofluid Dynamics Laboratory, The George Washington University,
- Department of Mechanical and Aerospace Engineering, The George Washington University
Abstract
Flow separation over a surface-mounted obstacle is prevalent in numerous applications. Previous studies of 3D separation around protuberances have been limited to steady flow. In biological and geophysical flows, pulsatile conditions are frequently encountered, yet this situation has not been extensively studied. Primarily motivated by our previous studies of the flow patterns observed in various human vocal fold pathologies such as polyps, our research aimed to fill this gap in the knowledge concerning unsteady 3D flow separation. This is achieved by characterizing velocity fields surrounding the obstacle, focused primarily on the vortical flow structures and dynamics that occur around a hemispheroid in pulsatile flow. As part of this study, two-dimensional, instantaneous and phase-averaged particle image velocimetry data in both steady and pulsatile flows are presented and compared. Coherent vortical flow structures have been identified by their swirling strength. This analysis revealed flow structures with dynamics dependent on the pulsatile forcing function. A mechanism to explain the formation and observed dynamics of these flow structures based on the self-induced velocity of vortex rings interacting with the unsteady flow is proposed.
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