GALCIT Colloquium

There are a variety of tools and methods available to identify and investigate coherent structures in a range of vortex-dominated fluid flows, from both computational and experimental data. Eulerian criteria, such as the Q or swirl, use the instantaneous velocity field and its gradient and give a good indication of the vortex cores. The definition of vortices, however, can be subjective, and they do not capture structure boundaries. Lagrangian techniques, such as the finite-time Lyapunov exponent, calculate criteria values along particle trajectories, making them more computationally expensive, but they can yield objective structure boundaries, features of which are used for structure identification, the study of structure evolution, and tracking. For a thorough investigation of unsteady, three-dimensional vortex-dominated flows, inclusion of both Eulerian and Lagrangian techniques are complementary and can provide the most information. This is demonstrated with results from both simulation and experiments of a circular cylinder in cross-flow, a simulation of a flat plate undergoing an unsteady pitch-up maneuver, and simulation of fully three-dimensional turbulence.