Effects of the distance between a vibrating cantilever pair

Two dimensional unsteady numerical simulations were conducted using a commercial code with a user-defined-function to investigate the effect of the distance between two cantilevers vibrating in counter-phase or in phase. The performance of the cantilevers with different distances was mainly evaluated by the time-averaged axial velocity and the mass flow rate. It is evident that there is no interaction between the vortices by two cantilevers if they are too far apart. However, if two cantilevers are too close, they hinder each other in vortex generation. In particular, the interaction between two inner vortices generates a reversed flow which has a negative effect on the performance. Unless the distance is too close, the performance of the cantilever pair vibrating in counter-phase is always superior to the cantilever pair vibrating in phase. The optimal distance between two cantilevers in counter-phase is approximately equal to twice the size of a fully-grown vortex generated by the single cantilever, while there is no distinct optimal distance for a cantilever pair vibrating in phase. In case the distance is larger than three times the vortex size, the flow field generated by each cantilever is similar to the flow field of a single cantilever, which implies that two cantilevers work independently of each other.