稀薄两相流模型及数值模拟方法研究

In the jet from the exit of hypersonic solid rocket engines, there are some particles of Al2O3, which are fired to the high-altitude atmosphere at an extremely high speed, and forms the so-called plume, because it is a jet stream of plume shape. After ejecting from the rocket exit, the plume expands rapidly into vacuum and develops a two-phase flow field consisting of gas molecules and Al2O3 particles. The presence of Al2O3 particles can produce extra aerodynamic and thermal loads of the spacecraft, and consequently has a significant effect on the aerodynamic properties and thermal protection system design. In addition, the backflow plume will contaminate some important components, such as lens, antenna and solar arrays. Therefore, it is necessary to accurately predict the two-phase plume flow. In the project, we are going to establish a particle-particle collision model to consider the effect of aspheric particles, and a gas-particle collision model to involve the two-way coupling associated with momentum and energy transfer between the gas and particle. Then, based on the Cartesian grid, we develop a rapid and accurate numerical method to model the rarefied two-phase flows, by employing non-uniform time step and non-uniform weight factor technique, and the recursive coordinate bisectioning dynamic load balance algorithm. Then, we apply the method to high-altitude jets/plumes produced by the solid rocket engine, aiming at predict the extra aerodynamic force/moment and aerothermal environment due to the two-phase flow. This study may benefit the development of the interdisciplinary rarefied gas dynamics and multi-phase fluid dynamics.

高空固体火箭发动机等产生的喷流中通常存在Al2O3颗粒，喷流经喷管加速，以非常高的速度向环境介质射去，形成羽毛状的燃气尾流，称之为羽流。在高空中高温羽流将迅速膨胀，形成气体-颗粒共存的两相流场。气体-颗粒共存的两相流场不但会影响飞行器的气动特性和防热设计，还会对飞行器表面造成羽流污染，故亟需准确预测稀薄流区高超声速飞行器喷流和羽流的两相流效应。本项目建立非球形颗粒碰撞模型和气体-颗粒碰撞模型，考虑非球形效应的颗粒-颗粒碰撞和气体与非球形颗粒之间动量、能量的双向耦合，基于自适应Cartesian网格技术，引入非均匀时间步长和非均匀权因子技术，结合递归坐标二分法仿真粒子动态负载平衡技术，发展稀薄两相流高效准确的数值模拟方法，实现高空固体火箭发动机的喷流/羽流等稀薄两相流的数值模拟，有助于准确预测羽流导致的气动力/力矩和气动热和羽流污染评估，并促进稀薄气体动力学/多相流流体动力学交叉学科的发展。

高空固体火箭发动机等产生的喷流中通常存在Al2O3颗粒，喷流在高空的稀薄大气环境中会迅速膨胀，形成稀薄气体和固体颗粒共存的两相流场。该两相流场不但会影响飞行器的气动特性和防热设计，还会对飞行器表面造成污染，故准确模拟这类稀薄气体和固体颗粒形成的两相流至关重要。本课题首先在现有DSMC方法的基础上，实现了网格的自动生成和自适应加密，结合非均匀权因子、非均匀时间步长和动态负载平衡等数值模拟技术，发展了一套高效的三维自适应DSMC方法。然后，建立了稀薄气体分子和非球形固体颗粒之间和动量/能量传递模型，实现了气体分子和固体颗粒双向耦合，发展了稀薄流区气体颗粒两相流高效准确的DSMC模拟方法。最后，还开展了稀薄来流与固体火箭发动机喷流两相流动的数值模拟，获得了来流/喷流两相流动的典型特征，研究了固体颗粒喷流密度和速度对流动特征和表面特性的影响规律和机理。结果表明：高温颗粒喷流阻挡高速来流，在喷口前方形成局部超高压和高热流区域，颗粒喷流的密度和速度的变化会改变喷口前方的分离区和漩涡结构等流场特征。此外，颗粒喷流密度和速度对表面特性也有重大的影响：喷流密度和速度越大，在喷口前方引起的压力和热流越大。