Uncovering large-scale coherent structures in natural and forced turbulent wakes by combining PIV,POD, and FTLE |
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Authors: | L?Kourentis Email author" target="_blank">E?KonstantinidisEmail author |
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Institution: | (1) Department of Mechanical Engineering, University of Western Macedonia, 50100 Kozani, Greece; |
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Abstract: | Planar velocity data of the unsteady separated flow in the turbulent wake of a circular cylinder obtained by particle image
velocimetry (PIV) are analyzed in order to visualize the large-scale coherent structures associated with alternating vortex
shedding at a Reynolds number of 2,150. Two different cases are examined: unforced vortex shedding in the natural wake and
vortex lock-on incited by forced perturbations superimposed in the inflow velocity. Proper orthogonal decomposition (POD)
is employed to reconstruct the low-order wake dynamics from randomly sampled snapshots of the velocity field. The reconstructed
flow is subsequently used to determine the evolution of the finite-time Lyapunov exponent (FTLE) fields which identify the
Lagrangian coherent structures. The results demonstrate that the combination of methods employed offers a powerful visualization
tool to uncover large-scale coherent structures and to exemplify vortex dynamics in natural and forced bluff-body wakes. |
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