Unified gas-kinetic scheme for the study of micro flows and high-order extension

Abstract

In this thesis, the unified gas-kinetic scheme (UGKS) method for monatomic gas flow simulations has been reviewed to study micro flow. UGKS is a multiscale method which utilizes the integral solution of the kinetic model equation with the discrete velocity space. The coupling of free transport and collision process leads the mesh size and time step not limited by the particle mean free path and collision time. This property makes the UGKS to be a great tool to study low-speed micro flows. The UGKS is reviewed and validated by few test cases. With the importance of thermal management within the Micro-Electro-Mechanical System for the desired device operation, the thermal transportation inside the oscillating cavity for various flow regimes is studied with UGKS. The heat flux computed by the constitutive relations is compared with the heat flux computed by the moments of distribution function from UGKS to show the limitations of the constitutive heat flux beyond the transition regime. Then, the oscillating effect inside the cavity is discussed. At last, the high-order UGKS (HUGKS) is introduced by implementing high order reconstruction on the equilibrium part of the UGKS, while the original second-order method is applied to the non-equilibrium part. Thus, HUGKS is expected to maintain the multiscale property by recovering non-equilibrium flow solutions in rarefied regime, and providing better results in the near continuum regime with higher order accuracy. The scheme is validated by some test cases, and it is expected to provide accurate solutions for micro flows in the near continuum regime.

Date of Award	2022
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Kun XU (Supervisor)