Research On The Fluid-structure Interaction Problems Of Bio-inspired Flexible Paltes

There is complicated motion control theory lies in the problem of common phenomenon in natural world like swimming and flying of biology. From the dynamics of fluid-structure interaction, study the mechanism in it will be benefit for understanding the mechanism of animal propulsion and designing novel bionic robots. This article uses the bionic flexible body as model to study its fluid-structure interaction problem by simulations and experiments. By varying constitutive and dynamics parameters of the flexible body and the fluid, the coupling mechanisms of flexible plate’s passive movement, semi-active movement, interactions between flexible plates and plate-cylinder interactions have been analysed. The findings of this work would offer some inspiration and theoretical basis for understand the mechanisms of biology swimming and flying, designing novel energy harvester and developing efficient biology swimming system.A novel immersed boundary-lattice Boltzmann method(IB-LBM) is used to model the fluid-structure interaction problem with biologically flexible structure. The small circulatory fluid-structure interaction experiment water tunnel has been designed, which can provide stable incoming flow for the fluid-structure interaction experiments of the flexible plates. The coupling of multiple passively flapping flexible plates has been studied. For the plates arranged in tandem, the upstream one can always enjoy drag reduction, but the downstream one has two different coupling situations of drag increase and decrease. For the plates in side-by-side arrangement, four different flapping modes have been displayed: single-plate mode, anti-phase mode, in-phase mode and decoupling mode, the dynamic and fluid characteristics are analysed. The plates can enjoy drag reduction in the in-phase mode, and exists of the in-phase mode strongly depends on the interval distance and reynolds number. For plates in triangular arrangement, four typical flapping patterns are shown, in most cases, two downstream plates flap synchronously, the phase difference between upstream and downstream plates is decided by the interval distance. When the distance of the three plates is small, all of them can enjoy drag reduction. Then the semi-active flapping plates is studied. The key factors and four typical flapping patterns are analysed in this part. The flapping frequency of the leading edge is found to having the crucial influence on the kinematics characteristics of the plate, faster the plate flaps, larger drag it experiences. The increasing of the bending rigidity can decrease drag and flapping amplitude of the trailing edge in a certain extent. At last, plate attachs a rigid cylinder and plate immersed in the wake of cylinder are studied. For the former, when the length of the plate is small enough, it will curl up because of the suction zone’s attraction, increasing of the bending rigidity could help to resist the attraction. The exists of the plates also has an influence on the position and shape of the suction zone. For plate immersed in the wake of cylinder, inverted flapping mode and forward flapping mode are shown in this part. In the inverted flapping mode, plate is attracted by the suction zone. In the forward flapping mode, the vortexes shedding by the cylinder have a strong influence on the plate’s flapping motion which enlarge the flapping amplitude and synchronize the flapping frequency of the plate. The upstream cylinder always enjoys drag decrease.