Three-Dimensional Simulations of Anisotropic Slip Microflows Using the Discrete Unified Gas Kinetic Scheme

Area of Science:

• Computational fluid dynamics
• Microfluidics
• Non-equilibrium gas dynamics

Background:

• Accurate simulation of microfluidic devices requires advanced boundary conditions.
• Existing slip boundary conditions may not fully capture complex flow behaviors in three-dimensional (3D) micro-geometries.
• Understanding anisotropic slip is crucial for optimizing micro-device performance.

Purpose of the Study:

• To propose and validate a novel anisotropic slip boundary condition for 3D simulations.
• To investigate the effects of anisotropic slip on the unsteady flow within a two-sided orthogonal oscillating micro-lid-driven cavity.
• To provide insights into the relationship between slip characteristics and flow dynamics.

Main Methods:

• Development of an anisotropic slip boundary condition with adjustable streamwise and spanwise slip lengths.
• Implementation of the boundary condition within the discrete unified gas kinetic scheme (DUGKS).
• Introduction of a 3D corner boundary condition to mitigate singularities.
• Numerical simulation of a two-sided orthogonal oscillating micro-lid-driven cavity flow.

Main Results:

• The proposed DUGKS method with anisotropic slip boundary conditions shows higher accuracy compared to lattice Boltzmann method approaches.
• Wall oscillation velocity has a lesser impact on normal velocity than tangential velocity components.
• Larger slip lengths generally exert a more significant influence on velocity profiles.
• Anisotropic slip on one wall can enhance 3D flow mixing more than uniform slip.
• Flow field influence depends on slip length and the relative direction of wall motion and slip velocity.

Conclusions:

• The novel anisotropic slip boundary condition effectively simulates 3D microflows.
• Anisotropic slip significantly influences flow patterns, particularly 3D mixing in oscillating micro-cavities.
• Findings aid in understanding unsteady microflow phenomena and designing advanced microdevices.