运载火箭燃料系统低温两相流动机理与热物理场分布特性研究

The new generation launch vehicle employs liquid oxygen and liquid hydrogen as propellant, and its fuel system will involve many scientific and technical issues relating cryogenics. In the ground precooling stage, the two-phase fluid from the engine precooling loopreturns back to the tank filled with supercooled liquid, which leads tomovement of fluid clusters companying with phase change. Therefore the flow process combines with the separation and condensation of gas cluster and the bubbling of liquid cluster. Due to the heat leakage, subcooled boiling may occur in the nearby region of tank wall, and the bubbles generated in this process will form a flow boundary layer. During the initial stage of rocket launch, the intense scour of tank ektexine by ambient gas will produce heat and permeate through the tank wall to get the cryogenic liquids warmed up. Passing through the atmosphere and the stratosphere, this aerodynamic heating will be largely influenced by the density as well as the velocity of the ambient gas. In this project, A transient thermophysical phenomenon during the bubble-moving and heat-mass transfer process within the supercooled liquid will be investigated by theoretical analysis and numerical simulation. The mechanism and characteristics in moving cluster and in aerodynamic heating layer will be emphasized. Moreover, the thermal stratification in the liquid tank will be attentively studied by simulation and measurement. An experimental platform will be established to examine the flow and heat transfer characteristics of high-velocity gas flow over an outer boundarywith the low-pressure (varying-density) condition. The main objective of this study is to reveal the mechanism and characteristics of cryogenic two-phase flow inside fuel tank and to gain an effective method for solving the corresponding flow and heat transfer, in an attempt to provide a theoretical and technical guideline for domestic research of new generation launch vehicles.

新一代运载火箭采用液氧液氢为推进剂，处于低温下的燃料系统会遇到大量的涉及低温的科学与技术问题。在地面预冷阶段，经发动机返回的两相流体进入贮箱，在过冷液体区形成了伴随相变的流团运动，产生气相分团、凝结及液体流团气泡化；由于漏热，在贮箱内壁附近会出现过冷沸腾，气泡在壁面处形成气泡流动边界层。火箭升空阶段，外界气体将对贮箱外壁产生强烈冲刷。随着飞行高度增加，气压降低、密度减小，外壁面气动热受速度和密度的共同作用会先增后减。本项目拟采用理论分析和数值模拟手段，研究过冷液体中气泡运动与热质传递过程中非稳态热物理问题、气化热边界层内部热物理问题；借助实验手段研究液体贮箱温度分层规律。建立实验平台，研究低气压（变密度）高流速外掠边界层流动与传热问题。通过研究，揭示燃料贮箱内部低温两相流动机理与规律，探索用于求解低温两相流动与传热问题有效方法，为我国自行研发新一代运载火箭提供理论和技术支持。

在新一代大型运载火箭中，由于存在低温液体燃料系统，使其带来了大量的涉及低温的科学与技术问题。本项目针对低温液氢/液氧贮箱，采用理论分析和CFD数值模拟技术研究了在地面停放、升空以及在轨运行整个周期中低温贮箱内部热物理场分布及流场运动规律。通过数值研究总结出了一套用于计算非稳态、有相变、大尺度空间、复杂流场的CFD简化处理和优化计算方法，实现了低温贮箱在整个运行过程中物理场的数值预测。研究发现，虽然微重力下的流体温度分层相较于大过载工况有所减弱，但仍存在明显的轴向热分层，从而限制了流体过冷度容纳外界热侵的能力。若能破坏箱内热分层，促使箱内流体温度均一化，则可最大限度地延缓压力升高。因此，搭建了在轨贮箱热力学排气系统（TVS）的地面实验平台，验证了地面条件下热力学排气系统的良好控压效果以及有效消除漏热的能力，丰富了国内有关TVS的实验研究。同时，在运载火箭升空期间，由于变压力、变密度、变飞行速度等多变参数的影响，采用传统计算方法已不能再准确预测绝热材料的绝热性能以及贮箱与大气的换热。针对某重型运载火箭低温贮箱复合绝热方式，对传统多层绝热材料预测模型进行了变大气温度、变层间压力的理论修正，并成功应用于升空阶段多层绝热层非稳态传热的准确预测；针对稀薄气体传热，搭建了一套压力和速度可控的低密度风洞试验台，并获得了压力和克努森数对外掠物体传热特性的规律，提出了一套预测稀薄气体传热的计算关联式。实验研究发现，连续流区时克努森数对换热的影响并不明显，但在滑移流区时克努森数和雷诺数对换热均有显著地影响。为了进一步深入探索滑移流区传热机理，构建了滑移流区壁面边界条件，完成了低压气体在滑移流区流动与传热的数值模型开发，并获得了滑移流区气体流动与传热特性规律。本项目还对大过热度下蒸气凝结换热、过冷低温推进剂获取方法、在轨补加等技术进行了研究，得到了满意的效果，为我国自行研发的新一代运载火箭提供了理论和技术支持。