effect of cilia beat frequency on muco-ciliary clearance

background: the airway surface liquid (asl), which is a fluid layer coating the interior epithelial surface of the bronchi and bronchiolesis, plays an important defensive role against foreign particles and chemicals entering lungs. objective: numerical investigation has been employed to solve two-layer model consisting of mucus layer as a viscoelastic fluid and periciliary liquid layer as a newtonian fluid to study the effects of cilia beat frequency (cbf) at various amounts of mucus properties on muco-ciliary transport problem. methods: hybrid finite difference-lattice boltzmann-method (fb-lbm) has been used to solve the momentum equations and to simulate cilia forces, and also the pcl-mucus interface more accurately, immersed boundary method (ibm) has been employed. the main contribution of the current study is to use an oldroyd-b model as the constitutive equation of mucus. results: our results show that increasing cbf and decreasing mucus viscosity ratio have great effects on mucus flow, but the effect of viscosity ratio is more significant. the results also illustrate that the relation between cilia beat frequency and mean mucus velocity is almost linear and it has similar behavior at different values of viscosity ratio.  conclusion: numerical investigation based on hybrid ib-fd-lbm has been used to study the effect of cbf at various mounts of mucus viscosity ratio on the muco-ciliary clearance. the results showed that the effect of viscosity ratio on the muco-ciliary transport process is more significant compared with cbf.