ABSTRACT

A dual bell nozzle (DBN) consists of two bell nozzles of different geometric area ratios attached at the region called inflection. This distinct geometry modification allows the nozzle to adapt to altitudes through its different operating modes. A numerical investigation with hot flow is done on a 2-dimensional axisymmetric model of a DBN having coolant injection at its inflection. Analysis has considered the secondary injection of gaseous hydrogen film into the gas mixture resulting from the combustion of liquid hydrogen and liquid oxygen in the thrust chamber of a LO2/LH2 engine. Model gave a root mean square deviation of 0.0012 from the experimental result at 30 NPR. Flow phenomena inside the nozzle are studied for different altitudes with and without coolant injection. Shift of separation location inside the nozzle on changing the quantity of gaseous hydrogen injected for three nozzle pressure ratios in the range of operation of the nozzle is calculated. The nondimensional shift in separation location is estimated to be 1.34 at 30 NPR, 1.10 at 45 NPR and 0.70 at 60 NPR. Temperature distribution on nozzle wall and cooling effectiveness of coolant on nozzle wall is determined with varying coolant mass flow rate for LO2/LH2 and LO2/RP1 rocket engines and the results are compared. The effectiveness of coolant for LO2/LH2 engine reduces from 1 to 0.78 on moving downstream of the nozzle whereas it reduces from 1 to 0.27 for LO2/RP1 engine. The study also predicts reduction in specific impulse of 5% for LO2/LH2 engine and 3.3% for the LO2/RP1 engine at MR = 15 due to the film cooling.

摘要

双钟形喷嘴 (DBN) 由两个不同几何面积比的钟形喷嘴组成，它们连接在称为弯曲的区域。这种独特的几何修改使喷嘴能够通过其不同的操作模式适应海拔高度。对在拐点处注入冷却剂的 DBN 的二维轴对称模型进行了热流数值研究。分析已经考虑了气态氢膜二次喷射到气态混合物中，这是由液态氢和液态氧在 LO2/LH2 发动机的推力室中燃烧产生的。模型给出的均方根偏差与 30 NPR 的实验结果相差 0.0012。研究了喷嘴内不同高度的流动现象，有和没有冷却剂喷射。计算了在喷嘴的操作范围内对于三种喷嘴压力比改变喷射的气态氢量时喷嘴内分离位置的偏移。估计分离位置的无量纲位移在 30 NPR 时为 1.34，在 45 NPR 时为 1.10，在 60 NPR 时为 0.70。对于 LO2/LH2 和 LO2/RP1 火箭发动机，喷嘴壁上的温度分布和喷嘴壁上冷却剂的冷却效率是根据不同的冷却剂质量流量确定的，并将结果进行比较。在向喷嘴下游移动时，LO2/LH2 发动机的冷却剂效率从 1 降低到 0.78，而 LO2/RP1 发动机则从 1 降低到 0.27。该研究还预测，由于气膜冷却，在 MR = 15 时，LO2/LH2 发动机的比冲量降低 5%，LO2/RP1 发动机的比冲量降低 3.3%。