In this project, the main goal is simulation and investigation of low Reynolds number flows (Re 1) in a cylindrical enclosure which is expanded and contracted in a specified time period. The angle of cylinder opening is assumed constant at all generations and time independent for a self-similar geometry. In fact, study of this case help us to have a good understanding of air flow pattern inside the acinus of human pulmonary organ. Alveoli constitute the gas exchange units necessary for oxygen and carbon dioxide exchange with capillary blood vessels which are embedded within the alveolar membranes. Considering the cases described above, initially tried to present the conditions and the parameters of the problem and then tried to introduce Lattice Boltzmann method and to compare this method with other methods applied to solve fluid mechanic problems. Finally, there is a complete discussion about all flow patterns inside an alveolar in various generations. Dimensions applied for these simulations are in accordance with recent measurements for adult humans. Results for the rigid wall simulation case illustrate that convection in the duct induces a shear flow across the alveolus opening, thus generating a recirculation region filling the entire alveolar cavity. Results for the moving wall case (real state) determine that the rhythmic wall motion induces a small portion of the flow travels along the alveolar walls during breathing period. Thus, the fundamental difference compared to the rigid alveolus case is that net convective traort from the duct into the alveolus now exists. Also, the resulting alveolar flow patterns are largely time independent and governed by the ratio of the alveolar to ductal flow rates. This ratio depends uniquely on geometrical configuration such that alveolar flow patterns may be entirely determined by the location of the alveoli along the acinar tree. Key Words: Alveoli, Periodic Flow, Lattice Boltzmann Method, Moving Curve Boundary Condition
