近临界区液氮低速喷射特性研究

Identity of Liquid Nitrogen Low-Speed Injection near Critical Point

针对低温推进剂在超临界环境中的喷射特性,以液氮为模拟介质,基于SRK状态方程和LES模拟方法开展数值计算研究,获得了4MPa压力下液氮跨临界射流的形态特征,射流密度分布规律与试验结果吻合良好。计算结果表明:在临界点附近,液氮射流表面会形成高比热容屏障,抑制射流内部流体温度升高,从而维持射流核心区稳定;核心区射流表面涡的形成和发展由斜压效应主导,随着射流向下游发展,斜压效应、体积膨胀和粘性效应三者对涡量输运的贡献趋于同一水平;液氮射流破碎后形成并维持大的“高密度块”形态,随着温度升高,密度块逐渐扩散消失。

Aiming at the spray characteristics of cryogenic propellant in the supercritical environment,using liquid nitrogen as the simulation medium,the numerical simulation was carried out based on SRK equation of state and LES method. The numerical results for shape of liquid nitrogen tanscritical jet at 4MPa were obtained,and the density distribution agreed well with the experimental results. The simulation results show that,a high specific heat capacity barrier is formed on the surface of liquid nitrogen near critical point,which can restrain the increase of fluid temperature and maintain the stability of the core region. The formation and development of vortex on the jet surface in the core region is dominated by baroclinic effect. With the development of jet flow downstream,the contribution of baroclinic effect,volume expansion and viscous effect to vorticity transport tended to the same level. As the liquid nitrogen jet was broken,some large high-density blocks were formed,and density blocks gradually diffused and disappeared with the increase of temperature.