Enhancing Flow Transport by Exciting Lagrangian Coherent Structures (Hayder Salman, UNC-CH)

Abstract: We extend ideas from nonlinear dynamical systems to identify and extract Lagrangian coherent structures in a two-dimensional unsteady flow-field behind a bluff-body. These Lagrangian structures correspond to a set of finite time attracting and repelling material lines whose criss-crossing forms a network of lobes. These lobes are known to evolve according to a well defined set of rules and can be exploited to provide a skeletal backbone for the study of flow transport. Using these techniques, we have conducted 2D numerical simulations for the flow around a bluff-body and were able to identify a transport barrier that inhibits cross-wake transport. This observation is backed by experimental evidence at moderately low Reynolds numbers. By introducing wall-mounted actuators to excite the flow at the Strouhal frequency of the large scale vortex shedding, an aperiodic flow regime was generated with no transport barrier within the wake. Our results demonstrate how localised actuation can be used to excite global instabilities providing enhanced transport by our Lagrangian coherent structures.

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This is an abstract of a talk to be presented at the 2004 SEAMS Workshop in Charleston, SC. For more information, visit the workshop's homepage at math.cofc.edu/SEAMS.