Numerical Study On Behaviors Of Membranes In Fluid Flows

Two-dimensional (2D) and three-dimensional (3D) shape and motion dynamics of biological membranes in different flows are studied numerically. The results and conclusions are briefly given as follows:(1) In our numerical study, fluid flows are solved by the Lattice Boltzmann method (LBM), deformation of the 2D membrane is solved by the Lattice Spring model (LSM) and deformation of 3D membrane model is solved by nonlinear Finite ele-ment method (nFEM). Multi-block strategy is also applied. Interpolate Bounce-back method(IBB) and Immersed boundary method(IBM) are used to couple the fluid flow and membrane model.(2) The LBM and LSM are used to simulate the dynamic sorting of capsule in two dimensional bifurcated channel flow, they are coupled by IBB. When a capusle is settled in this bifurcated channel flow which is driven by the pressure difference between the inlet and outlets, it may choose different outlet. A capsule with a specific rigidity will choose the outlet according to the pressure difference between the two outlets, and this mechanism is applied to sort the capsules with different rigidity.(3) The 3D dynamics of a nonspherical capsule in general flow is studied. In previous study, the capsule is only studied in simple shear flow, and several modes of the capsule, tumbling, swinging and tank-treading are found. We derived the governing equations of the capsule in general flow, and two key dimensionless numbers. The numerical simulations are performed to draw phase diagrams. A new mode transition, tumbling to swinging, and then to tumbling, is found. A possible mechanism is revealed.(4) The interaction between the two tandem flexible loops are investigated. The two loops may flap in the uniform flow. It is found that when the distance between the two loops is not too large, both of their drag forces are smaller than that of a single loop in uniform flow, and the drag force may abruptly decrease at a specific distance. The effects of flapping amplitude, mean flow field and elastic energy of the loops are investigated.