FTLE ridges reveal material transport barriers (repelling LCS) in the double-gyre flow
Computing... | max FTLE = —
The double-gyre is a canonical 2D chaotic flow: u = −πA·sin(πf(x,t))·cos(πy), v = πA·cos(πf(x,t))·sin(πy)·∂f/∂x,
where f(x,t) = ε·sin(ωt)·x² + (1−2ε·sin(ωt))·x. FTLE (finite-time Lyapunov exponent) measures
the stretching rate of infinitesimally separated trajectories. Ridges of the FTLE field (bright lines) are
repelling LCS — hyperbolic material lines that act as barriers to transport.
Passive tracers cannot cross these barriers, confirming their role as dynamical boundaries.