An objective-adaptive refinement criterion based on modified ridge extraction method for finite-time Lyapunov exponent (FTLE) calculation

摘要

Visualizing finite-time Lyapunov exponent (FTLE) efficiently and accurately has long been a research objective in identifying the coherent structures of turbulence or vortex flows. In this field, adaptive mesh refinement shows its effectiveness. The proposed objective-adaptive refinement (OAR) criterion can refine adaptive particles in the vicinity of FTLE ridges by a modified gradient climbing method. While error-based refinement methods suffer from ineffective refinement when the initial velocity field contains error, and refinement methods based on FTLE magnitude have issues with undulate ridges, our objective OAR criterion always steers the refinement toward the vicinity of FTLE ridges. Testing cases include Bickley jet, mild FTLE ridge and experimental single vortex, three-dimensional ABC flow. The results demonstrate that the proposed OAR criterion can give the right refinement region, and thus enhance computation efficiency, by means of accurate extraction of FTLE ridges.