Numerical Study Of Fluid-Structure Interaction Dynamics Of A Free Flexible Plate In Typical Simple Flow

In this manuscript,the dynamics of passively moving flexible bodies in two typical simple flows are investigated numerically.Specifically,the deformation and motion of a flexible fibre in a two-dimensional channel flow(Poiseuille flow),as well as the free-fall motion of large-stiffness flat and curved plates are studied.For a flexible fibre that is passively transported in a channel flow,we mainly discover the nonlinear coupling of the fluid inertia(Re),flexibility of the fibre(K),and channel width(W).Inside a wide channel(e.g.W=4),as K decreases,the fibre adopts rigid motion,springy motion,snake turn and complex mode in sequence.It is found that the fluid inertia tends to straighten the fibre.Moreover,Re significantly affects the lateral equilibrium location yeq,therefore affecting the local shear rate and the tumbling period T.For a rigid fibre in a wide channel,when Re exceeds a threshold,the fibre stays inclined instead of tumbling.As Re further increases,the fibre adopts swinging mode.In addition,there is a scaling law between T and Re.For the effect of K,through the analysis of the torque generated by surrounding fluid,we found that a smaller K slows down the tumbling of the fibre even if yeq is comparable.As W decreases,the wall confinement effect makes the fibre easier to deform and closer to the centerline.The tumbling period would increase and the swinging mode would be more common.When W further decreases,the fibres are constrained to stay inclined,parabolic-like or one-end bending configurations moving along with the flow.For the free-fall motions of flat and curved plates with large stiffness,the effects of curvature(e.g.bending angle α),dimensionless moment of inertia I*,and Reynolds number Re on the falling mode of the plate are explored.The curvature can significantly change the fall path of the plate.For a large-stiffness flat plate,with the increase of the dimensionless moment of inertia I*,fluttering mode,chaotic motion and tumbling mode appear in sequence.However,with large curvature(α≥ π/4),the plate will only appear in the fluttering mode.The modal difference between the small curvature plate and the flat plate at low Reynolds number is small;while at high Reynolds number,the critical dimensionless moment of inertia I*between modes decreases,that is,relative to the flat plate,the plate with small curvature is more prone to tumble.For the fluttering mode,with the increase of α,the lateral and vertical fluttering amplitudes decrease,the falling trajectory tends to a narrower profile,and the average falling velocity becomes slower.For the tumbling modes,the period of the plate increases as α increases.