| The ability to actively control large coherent vortices in the wake of an unsteady body is studied experimentally. This thesis initially considers a single airfoil in a uniform flow that is forced to oscillate sinusoidally about its aerodynamic center. The resulting wake is expected to be dominated by large coherent vortices (Bohl & Koochesfahani, 2009), (Schnipper, Andersen, & Bohr, 2009), (Jung & Park, 2005), (Godoy-Diana, Marais, Aider, & Wesfreid, 2009), (Gopalkrishnan, Triantafyllou, Triantafyllou, & Barrett, 1994). The wakes for several different oscillation waveforms are studied and a model describing the evolution of the vortices as they progress downstream is developed and compared to the experimental data. The investigation then expands to 2 airfoils in a tandem configuration where the upstream airfoil produces a predictable and well studied wake which the downstream airfoil attempts to modify in some prescribed manner. To interpret the resulting velocity field in both cases, custom vortex detection software is developed so that vortices may be accurately identified and characterized. The experiments take place in a re-circulating water channel and flow measurements are undertaken primarily using the particle image velocimetry (PIV) measurement technique. The vortex detection algorithm must, therefore, accommodate experimental PIV velocity vector fields. Given the large number of vector fields that are to be investigated, the detection algorithm should proficiently and automatically reject false vortices with minimal human intervention. |
