Abstract: In order to deeply understand the working performance in the hot water rocket motor，a numerical model of the flow field in the nozzle of hot water rocket motor is established. And the numerical model is validated via a sample case. According to the study of the flow field in the nozzle of the motor，it is found out that the pressure firstly drops to the saturated pressure corresponding to the initial temperature in the convergent section and then continuously decreases along the axial direction. Besides，the phase change occurs at the nozzle throat，where the main flow would change into a two-phase flow，and vapor volume fraction at the exit is over 99%. Then，the two-phase flow is transferred from a subsonic condition into supersonic flow after the throat because of the changing of sound speed. The flow process in the nozzle can be divided into three steps，which are single-phase flow step，flash evaporation step due to pressure derease and expand-accelerating step，respectively. Though it was similar to the conventional chemical rocket motor，it had a certain complexity because of the phase change.

Key words: Hot water rocket motor; Numerical simulation; Phase change; Flash evaporation

摘要： 为了更好地了解热水火箭发动机的工作特性，建立了热水火箭发动机喷管流动的数值计算模型，并通过算例进行验证。通过对发动机喷管内部流场的研究，发现收敛段中压力首先降到初始温度对应的饱和压强，然后继续降低，并且在喉部的位置开始发生相变，从而使流动变为气液两相流，而且喷管出口处气相体积分数高达99%以上；由于变声速的原因，可以使两相流的流动在喉部之后达到超声速；把喷管的流动分为三个过程:单向流动过程、降压闪蒸过程和膨胀加速过程，与常规的化学能火箭发动机相比有类似性，但是由于闪蒸相变的存在，使其存在一定的复杂性。

关键词: 热水火箭发动机；数值模拟；相变；闪蒸