Harmonic forcing of a laminar bluff body wake with rear pitching flaps

A numerical study on the response of a two-dimensional bluff body wake subjected to harmonic forcing imposed by two rear pitching flaps is performed. The generated rectangle at height-based Reynolds number $Re=100$ , characterised laminar vortex shedding. Two strategies are examined corresponding in-phase ‘snaking’ and out-of-phase ‘clapping.’ effects aspect ratio ( $AR=1,2,4$ ), flapping frequency, amplitude, flap length investigated. For snaking motion, strong fundamental resonance root mean square (r.m.s.) drag observed when forced near shedding frequency. clapping weak subharmonic applied twice frequency resulting in an increase lift r.m.s. whereas remains unaffected. Both resonances intensify concomitant for motion. Forcing away from resonant regimes, both motions result considerable reduction through symmetrisation propulsion mechanisms. formation dipoles per oscillation period due which weaken natural shedding, has been identified as main mechanism. single scaling parameter proposed collapse flow over wide range frequencies, amplitudes lengths. Finally, assessment performance revealed that more effective than snaking.