Lagrangian coherent structures in flow past a backward-facing step

This paper investigates flow past a backward-facing step (BFS) in duct at Reynolds number $Re = 5080$ based on height, mean inflow velocity and fluid kinematic viscosity. The configuration matches combustion experiment conducted by Pitz Daily 1983. High-resolution fields are obtained OpenFOAM direct numerical simulation, the field analysed Lagrangian approaches. Trajectories of particles areas interest high-order integration, used to compute finite-time Lyapunov exponents (FTLEs) polar rotation angles. coherent structures (LCSs) extracted using geodesic theory, including hyperbolic LCSs elliptic LCSs. We use complementary qualitative quantitative LCS analyses uncover underlying structures. Notably, we find that pathway which rarely diverge from adjacent is opened closed FTLE ridges determined periodic shedding vortices BFS. Two dominant with significant coherence, generated respectively separated boundary layer shear layer, self-sustaining comparable strength. Hyperbolic repelling act as transport barriers between cores vortices, thus playing major part entrainment process. Interactions these different geometric regions partitioned lead intrinsic complexity BFS flow.