低温液体火箭两相流管路中POGO压力波传播与与衰减特性研究

POGO phenomenon is an important dynamical problem of space vehicles, and has been plaguing the designers because of its deleterious effect on vehicle structure and manned crews. An effective way to POGO suppression is to lower the frequency of the propellant feedline by changing its dynamic characteristics. This proposed project is concerned with the behavior of oscillating gas-liquid two-phase flow in liquid rocket propellant feedline. And the prime objective is to explore ways of eliminating or suppressing POGO oscillation by systematically analyzing the propagation and attenuation characteristics of oscillations in cryogenic two-phase flows under the conditions with and without phase change. By means of synergistically combining theoretical analysis, numerical simulation and experimental method, the works of the proposed project will focus on 1) performing numerical simulations on the flow condensation heat and mass transfer process occurring when gas oxygen coexists with subcooled liquid oxygen based on analysis of bubble behavior and stress condition; 2) developing pressure wave propagation models to predict the oscillations occurred in the propellant feed line in view of the flow pattern characteristic of gas–liquid two-phase flow, and discussing the propagation mechanism, the attenuation characteristic as well as the influencing factors of pressure oscillation in cryogenic two-phase flow with phase change and variable void fraction by self-build code on MATLAB; and 3) setting up test facilities with different combinations of gas/cryogenic liquid schemes to experimentally study the distinct dynamic characteristics of the oscillating cryogenic gas-liquid two-phase flow in the same frequency range as POGO oscillations, and to verify the feasibility and effectiveness of numerical and theoretical studies. The present study is of great value in eliminating or reducing POGO oscillations to acceptable levels, and thus has a significant impact on improving the safety and reliability of launch vehicle. The research results can serve as guidelines for the design and operation of both spacecraft and launch vehicles.

POGO振动是液体火箭研制中必须解决的重要技术难题，改变推进剂管路动特性是抑制POGO振动的重要途径。本项目以液体火箭推进剂输送管路为研究对象，采用理论分析、数值计算与实验研究相结合的方法，研究有相变和无相变两种情况下振动在不稳定低温两相流体中的传播和衰减特性，探求抑制POGO振动的有效途径与方法。主要研究内容包括：1）针对管路内高温高压气氧在过冷液氧中的冷凝过程，结合气泡行为效应及受力分析，开展低温流体冷凝相变传热传质过程的数值研究；2）基于两相流流型特征，建立压力波传播模型，研究压力脉动在有相变、变干度低温两相流中的传递机理、衰减特性和参数效应；3）搭建低温两相流压力波测试平台，通过实验研究POGO振动频率范围内低温两相流管路中的动态传播特征，验证数值模型和理论模型的正确性。本项目研究对抑制液体火箭的POGO振动、提高飞行器的安全性和可靠性具有重要意义。

POGO振动是液体火箭研制过程中必须解决的关键问题，其产生与压力脉动在推进系统管路内的传播特性密切相关。本项目采用理论分析、数值计算和实验研究相结合的方法，研究了低温两相流中压力脉动的传播和衰减特性。. 主要研究工作包括：1）开展了气泡冷凝相变过程动力学与热力学分析，建立了涵盖气泡生长、脱离、运动和冷凝整个生命过程的理论模型，获得了高温气泡在过冷流体中的运动轨迹和直径变化规律。研究表明，注气孔径、液体流速和注气速率是影响气泡脱离的主要因素，而系统压力、液体过冷度对冷凝长度具有显著影响。当系统压力由0.1提高到0.4MPa时，气泡冷凝距离增加2.5倍，而当过冷度从5K增加到30K时，冷凝距离减少85%。2）针对低温流体流动冷凝过程开展了三维全管路非稳态数值模拟，并采用原理实验数据对模型进行验证，定量分析了冷凝过程气液两相分布。结果表明，给定气、液入口温度下，存在使气体完全冷凝的临界入口气液比；改变气孔布局、流速、增加弯管段、设置扰流件或凸出结构等措施，可以强化液氧管路气液相间换热、加速气体冷凝。3）利用两流体模型对流动冷凝过程压力波传输特性进行仿真分析，研究了压力波在变干度低温气液两相流中的传递机理、衰减特性及其对相间热质传递的影响，探索了POGO抑制措施。结果表明，单相流动演变为气液两相流动时，压力波传播速度会陡然降低，衰减率增加；随着入口含气率增加，波速逐渐趋于平缓；压力波具有色散特性，随着扰动频率增加，波速增大最终趋于定值，衰减系数则持续增加；提高气体流量、入口流速，可降低压力波传播速度、增大衰减程度，进而抑制压力波在管路中的传播。4）搭建了流动冷凝可视化与两相流压力波传播测试平台，研究了流动冷凝两相流流型动态变化、压力波传播规律及其影响因素。结果表明，冷凝特性与气相离散程度密切相关，离散程度越高，气体冷凝越快，冷凝长度越短；单气孔进气冷凝长度为0.35-0.76m，多气孔进气方式可使冷凝长度减小至0.27-0.56m。. 研究结果对抑制液体火箭POGO振动、提高飞行器安全性和可靠性具有重要意义。