Identification of Lagrangian coherent structures in the turbulent boundary layer
PAN Chong, WANG JinJun & ZHANG Cao
Institute of Fluid Mechanics, Beijing University of Aeronautics and Astronautics, Beijing
Using Finite-Time Lyapunov Exponents (FTLE) method, Lagrangian coherent structures (LCSs) in a fully developed flat-plate turbulent boundary layer are successfully identified from a two-dimensional velocity field obtained by time-resolved 2D PIV measurement.
Simple Microvec TR PIV system was used in this experiment (similar to educational system 2). CCD Camera with 640 x 480 pixels and 200fps was acting as a high speed camera and the 1.5W SSD Laser was set in continuous mode. See the setup on the left.
Particle images are analyzed by MircroVec with interrogation windows of 16×8 pixels and overlap rate of 50%. The software package MANGEN was used to calculate FTLE field. The fluid trajectories are obtained by advecting particles in PIV-measured velocity field with a 4th-order Runge-Kutta-Fehlberg integration algorithm.
Comparison of the capability of three vortex identification techniques, the FTLE method, the velocity vector method and the vorticity method.