Numerical Study Of Flexible Bodies In Uniform Flow

In this paper,the fluid-structure interaction method for flexible body is used to simulate the flapping mode and the drag reduction problem of two tandem flexible rings and a series flexible inverted flags in a two-dimension uniform flow numerically.The main work and research results of this paper are as presented follows:(1)The lattice Boltzmann method is used to numerically simulate the fluid flow.Two-dimensional finite element method is used to numerically simulate the deformation of two-dinmensional flexible loops and flexible inverted flags.In addition,the immersed boundary method is used to calculate the interaction forces between the coupled fluid and solid.(2)The interaction of two flexible loops in the uniform flow is numerically studied.The two flexible loops are fixed at the front end,and the rest of the flexible loops flap freely.The flapping and drag of the flexible loops arc investigated,it,is found that at a certain gap distance,the drag of the rear loop drop suddenly.The flow field regime is used to analyze the reasons for the sudden drag reduction.At the same time,it is found that the change of the tension stiffness affects the position of the drag drop of the rear loop.If the rear loop is allowed to move freely in the lateral direction,we find that within a certain distance range,the rear loop changes the vertical equilibrium position from the main place to the position with lower drag,and the drag reduction distance of the rear loop decrease.(3)The interaction of multiple flexible inverted flags in the uniform flow is numerical studied.The flexible inverted flag is fixed at the rear end and the rest of the flag can oscillate freely.The flapping and bending energy are investigated,it is found that for the simple tandem inverted flag,the flapping amplitude of the rear inverted flag is suppressed within a.certain distance.The flapping amplitude is reduced and therefore the drag and bending energy are reduced.In order to obtain more bending energy for the inverted flag,infinite tandem inverted flags with a periocdic boundary condition in the lateral direction are proposed.In both the in-line arrangement,and the staggered arrangement,we are able to increase the flapping amplitude of the rear inverted flag and obtain grearer bending energy.Through the study of the vortex merging mechanism of front and rear flags,the reason for the increase of amplitude and bending energy of the rear inverted flag is explained.Through the study of limited tandem inverted flags,the arrangements of the tandem inverted flags proposed here are able to obtain more bending energy.