Vertically clamped flexible flags in a Poiseuille flow

Vertically clamped flexible flags in an oncoming Poiseuille flow were numerically modeled to investigate the hydrodynamic interaction and dynamics of the flexible flags using the immersed boundary method. The number of flags modeled was increased step by step: a single flag, double flags, triple flags, and a large array of multiple flags were modeled. The flexible flags displayed a flapping mode or a fully deflected mode, depending on the relationship between the elastic inner force and the hydrodynamic force. The bending angle (α), flapping amplitude (A), and period (T) of the single flag decreased as the bending rigidity (γ) increased. In the double and triple flag systems, the bending angle of the first flag reached a steady state as the gap distance (d) increased. The gap distance affected the position of the flag relative to the vortical structures. The vortical structures merged and formed a large vortex. Small vortical structures penetrated the large gap to drive flag flapping and force flag bending. In a large array of multiple flags, all flags were present in the fully deflected mode for a small gap distance. As the gap distance increased, the interactions between the flags increased. The flags were significantly influenced by the inlet and exit conditions.