氮气在缩放喷管中非平衡自发凝结的数值研究

Numerical Research on Nitrogen Spontaneous Condensation in Converging-Diverging Nozzle

针对氮气在收缩型喷管中自发凝结的两相流动,采用经典成核理论来计算气液两相间的质量传递,选用Standard Redlich Kwong气体状态方程,忽略了气液相之间的速度滑移,利用商业软件CFX中的非平衡凝结模型进行了二维数值模拟。通过对成核率的量级、压力和带液量变化趋势及开始凝结的位置等模拟结果的分析,验证了模型和数值计算的有效性。进一步的数值模拟结果表明:相比于无凝结的绝热膨胀过程,相变释放潜热及气液之间的导热会加热气体,使得气流压力升高、马赫数降低。平衡凝结模型及非平衡凝结模型的对比显示,非平衡数值模型能够更好地揭示低温下氮气自发凝结的两相膨胀过程。

Assuming a homogeneous flow without velocity slip between gas and liquid phases, 2-D numerical simulation for predicting nitrogen expansion flow with spontaneous condensation in a converging-diverging nozzle is accomplished via the non-equilibrium model of CFX. The mass transfer between two phases is calculated with the classical nucleation model and the standard Redlich Kwong state equation. The magnitude of nucleation rate, pressure and condensate mass fraction distributions, and condensation onset are comparatively analyzed to verify the validation of the model. Compared with the adiabatic expansion without condensation, the flow is heated by the latent heat and thermal conductivity between gas and liquid phases to heighten pressure and lower Mach number. A comparison between equilibrium condensation model and non-equilibrium condensation model shows better prediction of the latter for nitrogen expansion with spontaneous condensation.