A Coupled Discrete Unified Gas Kinetic Scheme For Micro Flows And Heat Transfer

Microscale gas flow and heat transfer mechanism are important research objects in microelectromechanical systems(MEMS)research.Under the micro-scale premise,the feature size is reduced and the local Knudsen number is increased.The gas no longer strictly satisfies the continuity hypothesis.The traditional methods based on the continuity hypothesis has already failed.Most of the simulation algorithms are only applicable in certain specific watersheds.It is difficult to calculate the problems in different watersheds.At the same time,in the micro-scale transport and heat transfer process,there are usually some anomalies,such as diffusion slip effect,hot creep phenomenon and discontinuous temperature effect.The mesoscopic method developed in recent years-Discrete Unified Gas Kinetic Scheme(DUGKS)is a multi-scale simulation algorithm that can perform full basin simulation and is suitable for cross-scale problem research.Based on the original DUGKS,this paper proposes a double-distribution-function model and establishes a coupled DUGKS.For the microchannel flow problem,the macroscopic differences between the isothermal and non-isothermal channel trimming drive flows are studied,and the flow field characteristics of the unstressed and stressed microchannels in the whole basin are studied.The simulation results and linear Boltzmann results,DSMC and experimental results are in good agreement,indicating that the coupled DUGKS has the ability to simulate full basin flow.For the micro-scale heat transfer,this paper focuses on the anomalous physical phenomenon-thermal creep,explores the formation and flow characteristics of hot creep in different watersheds,and analyzes the micro-channel size,left-right temperature difference and internal pressure field.The discontinuous temperatureinduced flow study shows that different Knudsen numbers have a great influence on the formation of the flow vortex in each cavity.The larger Knudsen number will cause the vortex to gradually form at the corner.In the case of a fixed Knudsen number,the larger the ratio of the temperature,the more obvious the velocity and temperature slip effect of the boundary layer,but the effect on the formation of the flow vortex is small.The research results show that the coupled DUGKS has high precision in the whole watershed and has the ability to simulate multi-scale problems across watersheds.It is suitable for micro-scale research and can meet engineering requirements in terms of computational efficiency and accuracy.