The Wake of a Bluff body in Highly Pulsatile Flow: Effects of Freestream Inflow Frequency Open Access
Bluff body wake dynamics are widely studied due to their diversity of rich flow physics when subjected to various inflow conditions and perturbations. Highly pulsatile inflow has proven in our prior studies to generate interesting and unexpected wake dynamics. High-amplitude fluctuations in freestream velocity, or pulsations, occur in biological, geophysical, and engineering flows, e.g. blood flow, coastal flows, and gusting winds. In this study we examine the effect of the frequency of the large freestream fluctuations, ranging from vortex lock-in frequencies on the high end to quasi-steady wake configurations on the low end. The bluff body studied is a surface-mounted hemisphere, the radius of which is several times greater than the local thickness of the boundary layer on the mounting surface. A series of direct numerical simulations (DNS) supplement experimental studies performed using planar particle image velocimetry and hot-wire anemometry in a low-speed, pulsatile wind tunnel. Characterizations of wake structure, turbulence, and various wake regimes through a sweep of frequencies will be presented and compared. A framework for understanding external flow forcing extending from a typical steady flow wake to generation of a single vortex at high pulsation frequencies akin to vortex ring production will be introduced.
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