State Key Laboratory of Aerodynamics;
China Aerodynamics Research and Development Center;
Mianyang 621000;
Sichuan Province;
China;
China Aerodynamics Research and Development Center;
Mianyang 621000;
Sichuan Province;
China;
Lagrangian criterion; unsteady flow separation; finite-time Lyapunov exponent(FTLE); two-dimensional periodic flow;