Numerical simulation of secondary combustion affecting base flow of base bleed equipment
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摘要: 为研究二次燃烧对底排尾部流场的影响，建立了底排装置尾部流场的化学非平衡流数学物理模型。其中二次燃烧模型采用10组分25步反应的H2-CO燃烧模型，运用统一算法的思路编程求解二维轴对称方程组。数值模拟结果与实验结果较吻合。在此基础上，对尾部流场以及燃烧特性进行了数值预测, 结果表明：二次燃烧所释放的热能远大于排气本身的热能，对增压减阻的贡献可达78%。二次燃烧改变了尾部的温度分布规律，使温度峰值分布在两个回流区内。排气沿着两回流区间的狭缝流入剪切层发生燃烧。一部分混气回流入底部附近，其中氧气不充足，存在大量CO和少量H2未直接反应。一部分混气沿着剪切层流入下游以及主回流区内，氧含量逐渐增多，H2和CO被反应殆尽。结果可为进一步研究底排增压减阻提供参考。Abstract: In order to investigate the influence of secondary combustion for base flow field, a mathematical and physical model about base flow with chemical non-equilibrium for base bleed equipment is conducted. H2-CO combustion model which consists 10 components and 25 reactions is used for secondary combustion. Two-dimensional axisymmetric equations are solved using a set of uniform numerical process methods. Simulation results agree with experiment data well. based on this, base flow field and combustion characteristics are numerically predicted. The results show that heat energy released from secondary combustion is far more than heat energy from bleed gases. Secondary combustion has a huge contribution to increase base pressure. It changes the temperature distribution of base region. Bleed gases flow into the shear layer, then combustion occurs. Some mixed gases which flow into the bottom region burn incomplete, because the oxygen is not sufficient near the bottom. Some mixed gases which flow into the downstream and main recirculation zone burn complete, because the oxygen is sufficient. The results can be used as reference for further improvement of the base bleed.
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Key words:
- fluid mechanics /
- secondary combustion /
- chemical non-equilibrium flow /
- base bleed /
- base flow field
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图 4 底部面积平均压力随排气参数变化曲线图
Figure 4. Area-averaged base pressures with different injections
图 5 底部面积平均压力随排气参数变化曲线图
Figure 5. Area-averaged base pressures with different injections
图 8 尾部H2质量分数分布图(I=0.010 7)
Figure 8. Mass fraction of hydrogen in base region(I=0.0107)
图 9 尾部CO质量分数分布图(I=0.010 7)
Figure 9. Mass fraction of carbon monoxide in base region(I=0.010 7)
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