High-order Unified Gas-kinetic Scheme

TL;DR

This paper introduces a high-order unified gas-kinetic scheme (UGKS) that combines WENO-AO spatial reconstruction and a two-stage fourth-order time scheme, improving accuracy while maintaining computational efficiency for multiscale gas flow simulations.

Contribution

It develops a high-order UGKS by applying advanced spatial and temporal techniques to the equilibrium part, balancing accuracy and computational cost for complex and smooth flow structures.

Findings

Enhanced accuracy in simulating multiscale flows.

Preserves the multiscale property of original UGKS.

Validated with multiple numerical test cases.

Abstract

In this paper, we present a high-order unified gas-kinetic scheme (UGKS) using the weighted essentially non-oscillatory with adaptive-order (WENO-AO) method for spatial reconstruction and the two-stage fourth-order scheme for time evolution. Since the UGKS updates both the macroscopic flow variables and microscopic distribution function, and provides an adaptive flux function by combining the equilibrium and non-equilibrium parts, it is possible to take separate treatment of the equilibrium and non-equilibrium calculation in the UGKS for the development of high-order scheme. Considering the fact that high-order techniques are commonly required for continuum flow with complex structures, and the rarefied flow structure are relatively simple and smooth in the physical space, we apply the high-order techniques in the equilibrium part of the UGKS for the capturing of macroscopic flow evolution, and retain the calculation of distribution function as a second-order method, so that a balance of computational cost and numerical accuracy could be well achieved. The high-order UGKS has been validated by several numerical test cases, including sine-wave accuracy test, sod-shock tube, Couette, oscillating Couette, lid-driven cavity and oscillating cavity flow. It is shown that the current method preserves the multiscale property of the original UGKS and obtains more accurate solutions in several cases.