Characterization of peristaltic flow during the mixing process in a model human stomach

Numerical simulations are performed to investigate the characteristics of peristaltic flow in a model stomach during the mixing and digestion process. The geometrical model for the stomach consists of an axisymmetric tube of varying diameter with a wall at one end, representing the antrum and closed pylorus. The antral contraction waves (ACWs) that produce the peristaltic flow are modeled as traveling waves that deform the boundary and consequently the computational mesh. This geometrical model is implemented into the open source code OpenFOAM. A parametric study is performed in which the fluid viscosity, wave speed, wave width, and maximum relative occlusion are varied. The effect of these parameters on the retropulsive jet induced near the pylorus and the recirculation between pairs of consecutive ACWs is investigated. Both of these flow features contribute to the mixing and digestion process. The retropulsive jet is quantified by its peak velocity and length along the centerline. For each wave geometry, these quantities are found to be independent of the Reynolds number for low Reynolds numbers, while for Reynolds numbers exceeding one, the peak centerline velocity decreases and the jet length increases as the Reynolds number increases. Moreover, the velocity and pressure curves are found to scale with the wave speed at low Reynolds numbers. Between different wave geometries, scaling laws are proposed and tested for the peak centerline velocity and jet length. Particle tracking and vorticity plots show that mixing efficiency increases when the relative occlusion increases, as well as when the viscosity or wave width decreases