非恒定增压式微尺度拉瓦尔喷管流动特性

针对微尺度喷流在航天器运动状态切换时出现的非恒定增压变化,采用直接模拟蒙特卡洛(DSMC)方法对阶跃式增压和线性式增压两种模式下的微尺度拉瓦尔喷管流场进行了模拟,并对其变化过程中的流动特性进行了对比分析。结果显示：阶跃式增压会导致流动特性出现较大幅值的峰谷式波动,而线性式增压下的流动特性则呈现出线性变化的特点;黏性力对微尺度喷流的非恒定增压变化产生了重要的黏滞作用,在喉部扩张段至出口的流场中尤为明显;在设定的条件下,阶跃式增压过程中喷流产生的总冲量较线性式增压高59.5%,质量流量高74.7%,单位工质提供的冲量低约8.6%,波动性也高于线性式模型,阶跃式增压适用于系统需要较大推力改变运动状态且推进剂充足的情况,而线性式增压在系统精确微调或需要推进剂产生更高效能时具有明显的优势。

Unsteady pressure boost micro-scale Laval nozzle flow characteristics

Targeting the unsteady pressure boost of the micro-scale jet when the spacecraft motion state was switched, the micro-scale Laval nozzle flow in the stepped pressure boost and linear pressure boost modes was used to simulate by direct simulation of Monte Carlo (DSMC) method, and comparative analysis of the flow characteristics in the process of change was done. Results showed that step-type pressure boost could cause a large amplitude peak-valley fluctuation in the flow characteristics, while the flow characteristics under linear pressure boost showed the characteristics of linear change; the viscous force played an important role in the unsteady pressure boost of micro-scale jet, especially in the flow field from the expansion section of the throat to the outlet; the total impulse, mass flow rate produced by the micro-scale jet and the impulse provided by unit quality working medium during the stepped pressure boost process was 59.5%, 74.7% higher, and 8.6% lower than the characteristics in linear pressure boost process, meanwhile, the volatility of the stepped pressure boost process was more obvious than the linear pressure boost process. It can be seen that the stepped pressure boost mode is suitable for system that requires large thrust to change the motion state and has sufficient propellant, and the linear pressure boost has obvious advantages when the system needs to be fine-tuned precisely or the propellant is required to produce higher efficiency. These research conclusions provide an effective reference for the design and optimization of micro-scale nozzles under different system conditions.