KAPPA: Kinetic approach to physical processes in atmospheres library in C++

KAPPA, an open-source software library for the computation of thermodynamic and transport properties in non-equilibrium gas flows and species production rates, is presented. Thermodynamic properties rely on custom databases which describe the characteristics of atoms and molecules and interaction features. Mixture thermodynamic properties are formulated from species quantities. Species production rates are based on elementary chemical reactions and vibrational energy transitions. Transport properties are derived from kinetic theory which provides relationships for transport coefficients depending on the flow model. Several levels of non-equilibrium flow description are implemented: the detailed state-to-state (STS) approach, multi-temperature and one-temperature models. Sets of transport coefficients depend on the deviation from equilibrium; in the state-to-state model, they include state-resolved diffusion coefficients for each pair of vibrational states. A highly modular, object-oriented application program interface (API) has been developed. The adopted object-oriented programming paradigm (OOP), along with the implemented models of state-resolved physico-chemical relaxation rates, is presented. The design of the library allows it to be easily included in existing CFD codes and is aimed at code reusability and readability.本文提出了一款名为KAPPA的开源软件库，其可用于计算非平衡气流中的热力学与输运特性以及组分产率。该库的热力学特性基于定制数据库构建，该数据库用于描述原子、分子的属性及其相互作用特征；混合气体的热力学特性由各组分的物理量推导得出。组分产率的计算则基于基元化学反应与振动能量跃迁过程，而输运特性则由分子动理论推导而来，该理论提供了依赖于气流模型的输运系数相关关系式。该库实现了多套非平衡气流描述方案：详细态到态（state-to-state, STS）方法、多温度模型与单温度模型。输运系数的集合随与平衡态的偏离程度而变化；在态到态模型中，输运系数包含每一对振动能级的态分辨扩散系数。该库开发了高度模块化、面向对象的应用程序编程接口（Application Program Interface, API），本文同时介绍了所采用的面向对象编程范式（Object-Oriented Programming, OOP）以及所实现的态分辨物理化学弛豫速率模型。该库的设计使其能够便捷地集成至现有计算流体动力学（Computational Fluid Dynamics, CFD）代码中，旨在提升代码的可复用性与可读性。