火箭剩余推进剂排放过程的分析与模拟

为了减少空间碎片的产生,星箭分离后,需要在轨排放火箭末级贮箱内的剩余推进剂,分析表明,排放条件下的推进剂射流进入太空后,立即失稳破碎为大量液滴;液滴在高真空环境下扩散,它们的表面不断有气体分子蒸发,逐渐在箭体周围形成了一个由液滴和蒸气分子组成的羽流场.采取Lagrange方法追踪该流场中每个液滴的运动轨迹以及表面蒸发冷凝过程,利用直接模拟Monte Carlo方法计算蒸气分子的运动和碰撞,然后通过微观量的统计平均获得感兴趣的宏观流场、箭体表面的压力和剪应力分布等.为了检验稀薄蒸气算法、模型和程序,模拟了真空水射流周围水蒸气羽流场,获得的径向Pitot压力分布与Fuchs和Legge的实验数据的符合。在此基础上,分别模拟了CZ-4B火箭末级剩余燃料偏二甲肼在不同排放方式下的三维稀薄蒸气与液滴羽流场。计算表明:原排放方式的扰动力矩相当大,超出了火箭姿控范围,新排放方式的扰动力矩很小,处于火箭姿控范围之内。这些预测得到了飞行遥测数据的支持。

Analysis and simulation of discharging residual rocket Propellants in orbit

To diminish the generation of space debris,the residual propellants in the storage tank of a final-stage rocket have to be discharged after the satellite-rocket separation.An analysis shows that the propellant jets under the discharge conditions,once entering the space,will break up into a number of liquid droplets.The droplets diffuse in the high vacuum,while gaseous molecules successively evaporate from the droplet surfaces.This process yields a rarefied vapor and droplet field around the final-stage rocket.This article employs the Lagrange means to track trajectories and evaporation processes of the droplets,and employs the direct simulation Monte Carlo (DSMC) method to calculate motion and collisions of the gaseous molecules.Macroscopic quantities of interest,such as the flow fields,surface pressure,shear stress and heat flux,etc.,are obtained through statistically averaging the corresponding microscopic quantities.This scheme is validated to simulate a steam plume around a water jet into vacuum,and the calculated Pitot pressure distributions in the radial direction agree with Fuchs and Legge's measured data.The scheme is then applied to three dimensional rarefied vapor and droplet plumes arising from original and new manners discharging in orbit the residual fuel 1,1-dimethyl-hydrazine of a CZ-4B final-stage rocket.The calculation shows that the original manner may lead to quite large disturbance moments beyond the rocket attitude-control range,whereas the new manner very small disturbance moments within the range.These predictions are supported by the remotely measured data of flights