Abstract The development of new upper orbit thrusters using cryogenic propellants requires an improved understanding of the dynamics of oxidizer and fuel injection at near vacuum conditions before ignition. Due to the low ambient pressure, the propellants enter a superheated state and flash evaporation occurs. Flash boiling of cryogenic liquid nitrogen is studied experimentally on the newly developed test bench at DLR Lampoldshausen and numerically with a newly developed OpenFOAM© solver. Here, a one-fluid approach is selected where phase properties, such as density, enthalpy and saturation conditions are determined with the thermodynamic library CoolProp and tabulated before runtime. The phase change is modeled by the homogeneous relaxation model. For highly superheated jets the flow becomes supersonic and forms a shock after the injector outlet. The solver is validated with the aid of flashing acetone spray experiments where the shock structures are more clearly visible. The results show that the developed solver is capable to predict the all important gas dynamics by matching shock structure and spray angle to the experiment. The experiments using cryogenic liquid, however, do not reveal any shock structures but regions with low negative axial velocities can be identified on the jet centerline. A comparison with the simulations now demonstrates that shocks continue to persist but the respective shadowgraph signals may be obscured in these flows. The joint experimental and numerical study thus provides a consistent understanding of the observed flow features that govern the fluid dynamics and jet breakup of cryogenic flashing flows.

中文翻译：

---

闪蒸低温氮气的数值与实验分析

摘要 使用低温推进剂的新型高轨道推进器的开发需要更好地了解点火前近真空条件下氧化剂和燃料喷射的动力学。由于环境压力低，推进剂进入过热状态并发生闪蒸。低温液氮的闪蒸在 DLR Lampoldshausen 新开发的测试台上进行了实验研究，并使用新开发的 OpenFOAM© 求解器进行了数值研究。在这里，选择了一种单流体方法，其中使用热力学库 CoolProp 确定相属性，例如密度、焓和饱和条件，并在运行前制成表格。相变由均匀松弛模型建模。对于高度过热的射流，流动变成超音速并在喷射器出口后形成激波。求解器在闪蒸丙酮喷雾实验的帮助下得到验证，其中冲击结构更清晰可见。结果表明，所开发的求解器能够通过将冲击结构和喷射角度与实验相匹配来预测所有重要的气体动力学。然而，使用低温液体的实验没有揭示任何激波结构，但可以在喷射中心线上识别出低负轴向速度的区域。与模拟的比较现在表明冲击继续持续，但在这些流中可能会掩盖各自的阴影图信号。因此，联合实验和数值研究提供了对观察到的流动特征的一致理解，这些流动特征控制着低温闪蒸流的流体动力学和射流破裂。