Abstract
Large eddy simulations (LESs) of cavity ignition processes were performed in a 2D ethylene-fueled supersonic combustor with a single rear-wall-expansion cavity based on OpenFOAM. The ethylene combustion was modelled using a 35-step with 20-specie ethylene chemical mechanism, which had been validated by CHEMKIN calculations. The effect on the ignition process of different ignition sites inside the cavity was then studied. It was found that the rear region of the cavity floor is an optimized ignition site where successful ignitions will be achieved. According to different ignition behaviors, two flame extinguishing modes could be identified: blown-off extinguishing mode and flow dissipation extinguishing mode. Blown-off extinguishing mode mainly occurred after ignition near the cavity shear layer, in which the initial flame was blown off directly due to the high speed of the supersonic core flow. Flow dissipation extinguishing mode is likely to occur after ignition near the front and middle cavity floor as a result of severe turbulent dissipations and limited chemical reactions. The study indicates that the movement routine of the initial flame is important for the ignition process, including both moving towards a favorable flow field and forming a large heat release region along the movement.
目的
超燃冲压发动机的点火过程是超声速燃烧领域的 重要课题之一。目前, 针对超燃冲压发动机燃烧 室点火过程的研究以实验研究为主, 数值研究则 相对较少。本文旨在基于大涡模拟研究点火位置 对点火过程的影响, 并在此基础上分析导致点火 失败的原因。
创新点
1. 基于大涡模拟, 研究点火位置对点火过程建立 的影响; 2. 发现了流动耗散和直接吹熄两种熄火 模式。
方法
1. 基于CHEMKIN, 选择合适的化学反应机理; 2. 在简化化学反应机理的基础上, 利用大涡模拟 研究不同点火位置对点火过程的影响; 3. 分析数 值仿真数据, 寻找能成功实现点火的点火位置, 并探讨导致点火失败的因素。
结论
1. 在凹腔后缘处点火可以成功实现发动机点火; 2. 发现了两种点火失败的模式, 即流动耗散模式 和直接吹熄模式; 3. 流动耗散模式主要发生在凹 腔前缘和凹腔中部, 而直接吹熄模式主要发生在 剪切层中。
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Zun CAI and Yong-chao SUN designed the research. Yong-chao SUN and Zun CAI processed the corresponding data and wrote the first draft of the manuscript. Tai-yu WANG and Ming-bo SUN helped to organize the manuscript. Cheng GONG and Yu-hui HUANG revised and edited the final version.
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Yong-chao SUN, Zun CAI, Tai-yu WANG, Ming-bo SUN, Cheng GONG, and Yu-hui HUANG declare that they have no conflict of interest.
Project supported by the National Natural Science Foundation of China (Nos. 11902353 and 51706238) and the Postdoctoral Innovation Talent Support Program of China (No. BX20190091)
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Sun, Yc., Cai, Z., Wang, Ty. et al. Numerical study on cavity ignition process in a supersonic combustor. J. Zhejiang Univ. Sci. A 21, 848–858 (2020). https://doi.org/10.1631/jzus.A1900419
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DOI: https://doi.org/10.1631/jzus.A1900419