UnDiFi-2D: An unstructured discontinuity fitting code for 2D grids

UnDiFi-2D, an open source (free software) Unstructured-grid, Discontinuity Fitting code, is presented. The aim of UnDiFi-2D is to model gas-dynamic discontinuities in two-dimensional (2D) flows as if they were true discontinuities of null thickness that bound regions of the flow-field where a smooth solution to the governing PDEs exists. UnDiFi-2D therefore needs to be coupled with an unstructured CFD solver that is used to discretize the governing PDEs within the smooth regions of the flow-field. Two different, in-house developed, CFD solvers are also included in the current distribution. The main features of the UnDiFi-2D software can be summarized as follows: Programming language UnDiFi-2D is written in standard Fortran 77/95; its design is highly modular in order to enhance simplicity of use, maintenance and allow coupling with virtually any existing CFD solver; Usability, maintenance and enhancement In order to improve the usability, maintenance and enhancement of the code also the documentation has been carefully taken into account. The git distributed versioning system has been adopted to facilitate collaborative maintenance and code development; Copyrights UnDiFi-2D is a free software that anyone can use, copy, distribute, change and improve under the GNU Public License version 3. The present paper is a manifesto of the first public release of the UnDiFi-2D code. It describes the currently implemented features, which are the result of more than a decade of still ongoing CFD developments. This work is focused on the computational techniques adopted and a detailed description of the main characteristics is reported. UnDiFi-2D capabilities are demonstrated by means of examples test cases. The design of the code allows to easily include existing CFD codes and is aimed at ease code reuse and readability.本文介绍了开源（免费软件）非结构网格间断拟合代码UnDiFi-2D。UnDiFi-2D的目标是对二维流场中的气体动力学间断进行建模，将其视为零厚度的真实间断，这些间断界定了控制偏微分方程（Partial Differential Equations, PDEs）存在光滑解的流场区域。因此，UnDiFi-2D需要与非结构计算流体动力学（Computational Fluid Dynamics, CFD）求解器耦合，该求解器用于在流场的光滑区域内对控制偏微分方程进行离散化。当前发布包中还包含两款自研的CFD求解器。 UnDiFi-2D软件的主要特性可归纳如下： 编程语言 UnDiFi-2D采用标准Fortran 77/95编写，其设计采用高度模块化架构，以提升易用性与可维护性，并支持与几乎所有现有CFD求解器进行耦合； 易用性、可维护性与功能拓展 为提升代码的易用性、可维护性与拓展性，本项目同步对文档进行了精心打磨；同时采用Git分布式版本控制系统，以助力协作式代码维护与开发工作； 版权声明 UnDiFi-2D属于免费软件，任何人可依据GNU通用公共许可证（GNU General Public License, GPL）第3版的条款对其进行使用、复制、分发、修改与优化。 本文作为UnDiFi-2D代码首次公开发布的正式说明文档，阐述了当前已实现的各项功能——这些功能是十余年持续推进的CFD研发工作的成果。本文重点阐述了所采用的计算技术，并对代码的核心特性进行了详细说明；同时通过多个典型测试用例展示了UnDiFi-2D的性能与功能。该代码的架构设计便于集成现有CFD代码，旨在提升代码复用性与可读性。