Coherent structures over riblets in turbulent boundary layer studied by combining time-resolved particle image velocimetry (TRPIV), proper orthogonal decomposition (POD), and finite-time Lyapunov exponent (FTLE)

Li Shan¹, Jiang Nan^{1, †}, Yang Shaoqiong^{1, ‡}, Huang Yongxiang², Wu Yanhua³

(color online) Typical snapshots of the FTLE field distribution in the x–y plane in the TBLs: linear combinations of (a) and (c) all available modes over smooth surface and riblets, respetively; (b) the first 311 modes for the smooth surface; and (d) the first 280 modes for riblets.