Chen Weishan

Hydrodynamic performance and flow control of two flexible bodies in fish schooling-like configuration

Swimming in side-by-side configuration is common in the schooling of fish. In this work, the hydrodynamic performance of two flexible plates in side-by-side configuration is modelled and simulated. The simulations are implemented by an in-house parallelized algorithm, which fully coupling the lattice Boltzmann method (LBM) and immersed boundary (IB) mathematically. The Reynolds number scaled by the plates length and incoming velocity is 200 to 500 in our study, the transverse gap distance is varied from 0 to 5. The results show that the systems coupling motions and hydrodynamics properties are highly depended on the gap distance. Based on the evolutions of wake pattern, the motion modes can be classified as four types, which are single-plate mode, in-phase mode, anti-phase mode and decoupled mode. Also, we find that the drag coefficient for one plate are always equal to another, and the drag reduction is happened when the distance is in the regime corresponding to in-phase mode. This work may help us to develop the novel underwater robots inspired by fish locomotion.

Hydrodynamic interactions between a cylinder and an attached elastic plate

An elastic plate behind a rigid cylinder in viscous flow is modeled numerically by an immersed boundary-lattice Boltzmann method (IB-LBM). The hydrodynamic interactions of a upstream cylinder and a adjacent passively flapping plate are studied by varying the length and bending stiffness of the plate. Two patterns of the plate are found in the simulation results, if the plate is short enough, it would curl up because of the attraction of the suction zone behind the cylinder. With the increase of the plates length, it will stretch and flap in a stable period. The cylinder has a strong influence on the dynamics of the plate and the plate also changes the vortex shedding of the cylinder and the shape of suction zone. With a downstream adjacent plate, the cylinder can always enjoys a drag reduction, longer the plate is, less drag the cylinder experiences. The vortex shedding frequency of the cylinder is larger than that of the single cylinder and equal to the plates flapping frequency. This study may help to understand the energy saving of flexible bodies stay in the wake of a rigid structure and the hydrodynamic interactions between them.