Eulerian and Lagrangian methods for coherent structure analysis in both computational and experimental data

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, which use the instantaneous velocity field and its gradient, are less computationally intensive and give a good indication of the vortex cores, but the definition of vortices can be subjective and they do not capture structure boundaries. Lagrangian techniques calculate criteria values along particle trajectories, making them more computationally expensive, but they yield objective structure boundaries. For a thorough investigation of both numerically simulated and experimentally measured vortex-dominated flows, inclusion of both techniques can provide the most information. Using the Lagrangian techniques, however, necessitate a careful consideration of the spatial and temporal resolution of the data to be analyzed. This is demonstrated with results from both simulation and experiments of a circular cylinder in cross-flow, direct numerical simulation of a fully turbulent channel, and Large Eddy Simulation of a turbulent jet.