An Open-source Solver to Model the Catalytic Decomposition of Monopropellants for Space Thrusters

ABSTRACT: This paper presents a solver for the CFD (computational fluid dynamics) modeling of catalytic chambers in monopropellant thrusters based on the open-source OpenFOAM® (Open Field Operation and Manipulation) framework. A model was formulated and used to simulate the physical and thermochemical processes taking place inside the catalytic chambers of the monopropellant thrusters. The code integrates reacting gas flow in porous media, with mass and heat transport. The most important implemented functionalities were the separation of two reactive gases, one transient reactive gas flowing between the catalyst bed interstices (interstitial gas), and another static reactive gas on the surface of catalyst particles, or pellets (surface gas). Homogeneous and heterogeneous reactions occur on the interstitial gas and the catalyst particle, respectively. A flexible definition of porous properties, a calculation of multicomponent diffusion-flux mass, a diffusion mass coeffcient, a mass transfer coeffcient, and a heat transfer coeffcient were implemented as well. Experimental and analytical studies about hydrazine monopropellant thrusters in the literature were used to the case tests and verification of the solver. Temperature and mass fraction fields were simulated and compared. The results of the temperature profile are in agreement with experimental and theoretical studies found in the literature, and mass fraction presents some differences.

摘要：本文基于开源OpenFOAM®（Open Field Operation and Manipulation，开放场操作与操控）框架，提出了一款用于单组元推力器（monopropellant thrusters）催化腔计算流体动力学（computational fluid dynamics，CFD）建模的求解器。本文构建了专用模型，用于模拟单组元推力器催化腔内部发生的物理过程与热化学过程。该求解器代码集成了多孔介质（porous media）内反应气流的流动过程，以及质量与热量输运过程。本求解器实现的核心功能之一是对两种反应气体进行差异化建模：一种是在催化剂床层间隙中流动的瞬态反应气体（间隙气体，interstitial gas），另一种是附着在催化剂颗粒（或丸粒）表面的静态反应气体（表面气体，surface gas）。均相反应（homogeneous reaction）与多相反应（heterogeneous reaction）分别发生于间隙气体与催化剂颗粒表面。此外，本求解器还实现了多孔介质特性的灵活定义、多组分质量扩散通量计算、扩散质量系数、传质系数以及传热系数的计算功能。本文采用文献中关于肼类单组元推力器的实验与分析研究成果，对该求解器进行了算例测试与验证。研究对温度场与质量分数（mass fraction）场进行了模拟并开展对比分析。温度分布的模拟结果与文献中的实验及理论研究结果吻合良好，而质量分数的模拟结果则存在一定差异。