The Interaction Between Flexible Plates And Fluid In Two-dimensional Flow

The interactions between fluid and flexible bodies exist in nature,everyday life and various industry applications.By investigating these phenomena,we can reveal the mechanism of flow induced vibration of flexible bodies,understand the process of energy exchange between flexible bodies and fluid,and learn the way flexible bodies interact with each other in a flowing fluid.The study on the interaction between flexible bodies and fluid not only makes us better understand the nature,but also helps us invent new machines or improve existing devices to harvest more energy from nature.In this dissertation,the interaction between a two-dimensional flexible plate and a fluid was researched in the soap film tunnels.The main topics discussed are as follows:1.The experiments of a single flexible filament flapping in a uniform flow were conducted.The basic experimental process,the data handling and the basic theoretical methods with respect to the analysis of the interaction between fluid and flexible body were investigated,making a base for the studies of more complex phenomena.2.A theoretical model of the interaction between two parallel flexible filaments in a uniform flow was proposed.The mechanism of the coupling modes between two filaments was explored in terms of linear instability analysis.Two special cases were studied and the distributions of the coupling modes in the non-dimensional and dimensional parameter spaces were predicted theoretically.The qualitative accordance with the experimental results was achieved.3.The experiments of the interaction between two tandem filaments in the soap film were conducted.It was found that the filament downstream slaloms in the vortex street shedding from the upstream filament.The force and energy were calculated in terms of an Euler-Benoulli beam model.The results showed that the downstream filament extracts energy from the flow to increase its kinetic energy,while the upstream filament is influenced little in this process.4.The flapping of a flexible filament in the wake of a cylinder was investigated experimentally in order to study the behavior of a flexible body in periodic flow. Three response modes that depend on the distance between the cylinder and the filament were observed in the experiments.They are the propulsion mode,swing mode and rock mode.A primary explanation on these modes is given in terms of the waving plate theory.In this dissertation,the interaction between a flexible body and fluid in a uniform or periodic flow,and the interaction between two flexible bodies in parallel or tandem were investigated experimentally and theoretically.In addition,the soap film tunnel apparatus,flow parameters and filament's properties measurement,flow visualization, and tiny force measurement technique were discussed in detail.