اسعد علیزاده

In the present study, the dynamics of a red blood cell (RBC) in a simple microchannel and in a microchannel with step stenosis is simulated using combined lattice Boltzmann- immersed boundary (LB-IB) method. The RBC is considered as a deformable boundary immersed in the fluid flow. The effects of plasma viscosity on the motion and deformation of the RBC was investigated. Then the motion of a circular RBC in a Poiseuille flow was analyzed. Since the RBC is put at the centerline of the channel and the flow in the channel is axisymmetric, the lift forces acting on the top and bottom part of the RBC are in equilibrium. When passing over a step stenosis in the channel the normal RBC was found to be more deformable and take higher speed as compared to the less deformable RBC. In addition, the normal RBC experienced tank-treading motion due to its low elastic and bending coefficients whereas for the less deformable RBC the tumbling motion took place. The current results showed reasonably good agreement with the available numerical results.

In this paper, motion of a flexible membrane and hydrodynamic interaction of multiple membranes in a microchannel are simulated by developing a computer code written in C. The membranes are considered as flexible boundaries immersed in the fluid. First a single biconcave shaped membrane with high rigidity is considered. Due to the rigidity of the membrane, it experiences tumbling motion and its vertical displacement becomes oscillatory. Then, the effects of initial position of a circular membrane on its deformation, vertical velocity and displacement are investigated. It was observed that as the initial location of the membrane approaches the channel’s central axis, its vertical displacement and velocity decreased, but its horizontal velocity component increased. Finally, the simultaneous motion of multiple membranes in a microchannel and their interaction with each other and with flow are evaluated. The membranes do not collide and hence the collision mechanism is not modeled. It was found that the upstream membrane experienced greatest deformation and the greatest force was exerted on it by the fluid on it. In addition, simultaneous presence of multiple membranes would result in a reduction in the flow velocity. The current numerical results have good agreement with the available valid numerical ones.

In the current study, the motion and deformation of an elastic membrane in a two-dimensional channel with and without a groove is simulated using a combined lattice Boltzmann-immersed boundary method. The lattice Boltzmann method is used to solve the fluid flow equations and the immersed boundary method is used to incorporate the fluid-membrane interaction. The elastic membrane is considered as a flexible boundary immersed in the flow domain. In the immersed boundary method, the membrane is represented in the Lagrangian coordinates while the fluid domain is discretized on a uniform fixed Eulerian grid. The interaction between the fluid and the membrane is modeled using Dirac delta function. The effects of no-slip boundary condition are enforced by addition of a forcing term to the lattice Boltzmann equation. Depending on the flow rate, the initial location and stiffness of the elastic membrane, the size of the groove, the membrane only rotates inside the groove or the flow moves it out of the groove. The results are presented in terms of flow velocity and pressure fields and membrane configuration at different times. Comparison between the present results and the available numerical and experimental ones shows good agreement between them.