# High-order gas-kinetic scheme in curvilinear coordinates for the Euler and Navier-Stokes solutions

## TL;DR

This paper develops a high-order gas-kinetic scheme in curvilinear coordinates for accurate simulation of Euler and Navier-Stokes flows in complex geometries, validated through various numerical tests.

## Contribution

A two-stage fourth-order gas-kinetic scheme in curvilinear coordinates is proposed, enabling high-accuracy flow simulations in complex geometries.

## Key findings

- Achieves high-order accuracy in curvilinear coordinates.
- Successfully simulates flows with strong discontinuities.
- Maintains geometrical conservation law in non-orthogonal meshes.

## Abstract

The high-order gas-kinetic scheme (HGKS) has achieved success in simulating compressible flow in Cartesian mesh. To study the flow problem in general geometry, such as the flow over a wing-body configuration, the development of a three-dimensional HGKS in general curvilinear coordinates becomes necessary. In this paper, a two-stage fourth-order gas-kinetic scheme is developed for the Euler and Navier-Stokes solutions in the curvilinear coordinates. Based on the coordinate transformation, the kinetic equation is transformed first to the computational space, and the flux function in the gas-kinetic scheme is obtained there and is transformed back to the physical domain for the update of conservative flow variables inside each control volume. To achieve the expected order of accuracy, the dimension-by-dimension reconstruction based on the WENO scheme is adopted in the computational domain, where the reconstructed variables are the cell averaged Jacobian and the Jacobian-weighted conservative variables, and the conservative variables are obtained by ratio of the above reconstructed data at Gaussian quadrature points of each cell interface. In the two-stage fourth-order gas kinetic scheme (GKS), similar to the generalized Riemann solver (GRP), the initial spatial derivatives of conservative variables have to be used in the evaluation of the time dependent flux function in GKS, which are reconstructed as well through orthogonalization in physical space and chain rule. A variety of numerical examples from the order tests to the solutions with strong discontinuities are presented to validate the accuracy and robustness of the current scheme. The precise satisfaction of the geometrical conservation law in non-orthogonal mesh is also demonstrated through the numerical example.