超临界燃油喷射近场结构与流量特性研究

Nearfield Flow Characteristics of Kerosene Injection at Supercritical Pressures

关键词:  航空发动机  燃烧室  超临界燃油  喷射特性  欠膨胀  近场结构

Key words:  Aeroengine  Combustor  Supercritical kerosene  Injection characteristics  Under-expansion  Nearfield flow structure

摘要:

组合发动机中燃油常处于超临界状态喷射入燃烧室中，其喷射特性决定着燃烧效率与稳定性。通过数值模拟系统地研究了滞止压力（2.5~3.5MPa），滞止温度（640~740K），环境压力（0.1~2.1MPa）及真实气体效应对超临界燃油喷射近场结构与流量的影响规律。研究结果表明：当环境压力小于声速临界压力时，射流近场产生膨胀扇区，膨胀扇区径向边界上存在低于环境温度的环形低温区；膨胀扇区的长度与直径均随滞止压力或滞止温度的升高而增大，随环境压力的降低而显著增大，且会出现由中度欠膨胀向极度欠膨胀的转变；燃油质量流量随滞止压力的升高而增大，随滞止温度的升高而减小，是否受环境压力影响取决于燃油流动是否处于壅塞状态；当滞止温度低于临界温度时，喷嘴内部会出现冷凝现象，流量明显提升；相较于理想气体模型，真实气体模型得到的燃油出口质量流量较高，射流核心区长度较小。

Abstract:

In combined aero-propulsion engines， kerosene is typically injected into the combustion chamber at supercritical pressures. The injection characteristics are essential to the subsequent combustion efficiency and stability. Numerical simulation is carried out to systematically investigate the impacts of stagnation pressure （2.5~3.5MPa）， stagnation temperature （640~740K）， ambient pressure （0.1~2.1MPa） and real gas behavior on the nearfield flow structure and mass flow rate of kerosene injection at supercritical pressures. The results reveal that a fan-shaped expansion zone exists at injection nearfield when the ambient pressure is lower than the choked critical pressure， with a thin low-temperature zone at the radial boundary of the expansion sector. The length and diameter of the expansion sector increase with increasing stagnation pressure or stagnation temperature. The expansion sector enlarges significantly with decreasing ambient pressure， with a transition from moderately to extremely under-expanded mode. Fuel mass flow rate grows with increasing stagnation pressure and diminishes with increasing stagnation temperature， while its dependence on ambient pressure relies on whether the flow is choked. When the stagnation temperature is below the thermodynamic critical temperature， condensation occurs inside the injection nozzle， leading to the notable increase of mass flow rate. Compared to the ideal gas model， the real gas model yields a higher mass flow rate at the nozzle exit and a smaller jet core length.