Lagrangian-Based Investigation of Unsteady Vertex Structure Near Trailing Edge of a Hydrofoil

Vortex shedding in turbulent flows is ubiquitous in our daily life and engineering applications. It is important to investigate the flow structures to predict their dynamical behaviors effectively. Lagrangian coherent structures (LCS) defined by the ridges of the finite-time Lyapunov exponent (FTLE) was utilized in this study to elucidate the time-dependent turbulent flows around a Clark-Y hydrofoil. The numerical simulation was performed with the commercial code CFX, and the turbulence modeling was carried out with the large eddy simulation (LES) approach in a classical eddy viscosity subgrid-scale (SGS) turbulence model. Comparing with experiment, the numerical simulation expressed its rationality and veracity. The results show that vortex shedding can lead to changes of pressure distributions near the trailing edge and the hydrodynamic fluctuations. The ridge of the FTLE field can form a LCS to represent a barrier between particles trapped inside the vortex region and those moving downstream. The results also indicate that the FTLE field has the potential to identify the unsteadiness of trailing edge vortex structures, and the LCS can capture the interface/barrier or the vortex region, such as trailing edge vortex and vortex street in the wake.