Synchronization of flagella

Motivated by the observed coordination of nearby beating flagella, we use highly controlled simple model experiments with rotating paddles to study how hydrodynamic interactions can lead to phase-locking. The agreement between our numerical models and experimental results confirms that hydrodynamic interactions can lead to synchronization or phase-locking if the system has sufficient flexibility. We also present a simple theory, valid for weakly interacting paddles, for both viscous and viscoelastic fluids.