环境压力对超临界流体喷雾特性影响的数值分析

摘要

Large eddy simulation was conducted to explore the supercritical injection process, in which thermal and transport properties were calculated with the SRK real gas state equation.The cryogenic nitrogen injection into a constant volume chamber was used to investigate the influence of ambient pressure on supercritical spray characteristics.Results show that large density gradient is formed around the jet surface as the large density ratio between the jet and surrounding gas prevents the jet to expand in the radical direction.With the increasing of environment pressure, the density ratio decreases.As a result, the jet surface becomes more unstable and vorticities are easily formed.This indicates that the higher chamber pressure has a positive effect on the mixing between the jet and the environment gas.The fact that the liquid core is shortened by increasing the chamber pressure further suggests that the higher environment pressure promotes the mixing process.Furthermore, it is also found that the ambient pressure has obvious effects on the thermal and transport properties, but little effects on the turbulent and velocity field.%基于大涡模拟方法对超临界喷射进行数值分析, 使用真实气体状态方程SRK计算流体的热物性和输运特性.研究对象是定容弹内低温液氮超临界喷射, 假定初始入口条件不变, 重点考察了不同环境压力对超临界喷雾特性的影响.结果表明:由于射流流体与周围流体之间存在较大密度比, 射流表面形成显著的密度分层, 并起到限制射流流体向径向扩展的作用.随着环境压力的提高, 由于射流和周围环境的密度比降低, 射流表面不稳定增加, 比较容易形成不稳定涡, 从而更有利于射流与周围气体的混合, 因而液核长度也比较短, 表明随着压力的增大, 射流与周围气体的混合效果更好.进一步分析发现, 环境压力对热物性和输运特性的影响较大, 而对湍动能和速度场的影响不大.