Numerical simulation of motion characteristics of flexible fresh tea leaf in Poiseuille shear flow via combined immersed boundary–lattice Boltzmann method

In this study, the deformations and trajectories of elastic fresh tea leaf in a simple straight channel model are investigated using the combined immersed boundary–lattice Boltzmann method (IB–LBM). The objective is to qualitatively analyze the effects of gravity, diameter and the Reynolds number (Re) on the physical characteristics of flexible fresh tea leaf, which is driven by Poiseuille airflow in a channel model. The LBM is used to simulate the fluid domain with regular Eulerian grid, while the IB method is employed to model the fluid–membrane interaction, with a set of Lagrangian moving grids being adopted for the fresh tea leaf. Our results mainly reveal that a tea leaf undergoes deformation due to the shearing effect of the Poiseuille flow, resulting in lifting of the leaf toward the channel center. Under the influence of gravity, the leaf performs a tumbling motion with clockwise rotation and preserves an oscillating stable state. Furthermore, the diameter has a far greater influence on the dimensionless shape parameters than Re. For a leaf of a certain size and position, a series of relations between L∕W and Re are established at various ratios of fresh leaves by least square method. Based on the above findings, such studies provide useful data and insights to obtain high-quality green tea by selecting mechanical-plucked fresh tea leaves according to shape consistency.