直接模拟蒙特卡罗羽流模拟的两相作用模型

Two-phase coupled model for DSMC plume simulation

关键词:  直接模拟蒙特卡罗  两相羽流场  气体-表面反射  漫反射  镜面反射

Key words:  Direct Simulation Monte Carlo(DSMC)  Two-phase plume field  Gas-surface reflection  Diffuse reflection  Specular reflection

摘要:

为了数值模拟包含气体分子和凝相颗粒的两相羽流场,使用自主开发的羽流计算软件(PWS)对两相作用模型进行研究。计算均匀气流对颗粒的加速过程,结果与理论解一致,证明气体分子对颗粒的单向作用模型合理。计算气体分子在颗粒表面的反射时,将全局坐标系转换到颗粒坐标系确定其法线,再转换到法线坐标系进行镜面反射或漫反射。将这种间接法与使用反射向量的分布函数的直接法进行了对比。对同一个气体分子在颗粒表面的反射进行1×10⁶次数值试验,两种方法所得镜面反射的速度向量均符合空间均匀分布,漫反射的速度向量分布相互一致。使用两种方法模拟150N液体火箭发动机的两相羽流场,所得气相羽流场几乎相同,间接法计算效率较高。液滴颗粒对气流场的影响主要集中在轴线附近,与无液滴的气流场相比,有液滴时会使气流温度升高、压强增大、马赫数减小。

Abstract:

To numerically simulate two-phase plume field with gas molecules and particles, self-developed Plume Work Station (PWS) based on Direct Simulation Monte Carlo (DSMC) method was used to evaluate two-phase coupled models. Particles introduced to a uniform gas stream were computed. The obtained DSMC solution is in agreement with the analytic solution, proving that the gas-particle one-way coupled model is reasonable. The gas-surface reflection was computed by an indirect manner. Firstly the global coordinate system was transformed to local particle system, and the normal direction was determined. Then the specular reflection or diffuse reflection was conducted in the normal coordinate system. Another way was to use known distribution functions of reflection vectors directly. 1×10⁶ numerical tests were conducted for the same gas-surface reflection using both approaches. Results of specular reflection satisfy the spatial uniform distribution, and results of diffuse reflection match well. Two-phase flow field of 150N liquid rocket engine was also simulated in two ways. Gas fields given by two methods are almost the same. The computation efficiency of indirect method is a little higher. The liquid droplets affect the plume field only near the axis line of the engine. The plume temperature and pressure increase and Mach number decreases by comparing to the computational results without droplets.