High-fidelity geometry models for improving the consistency of CHAMP,GRACE, GOCE and Swarm thermospheric density data sets

During the last two decades, accelerometers on board of the CHAMP, GRACE, GOCE and Swarm satellites have provided high-resolution thermosphere density data to improve our knowledge on atmospheric dynamics and coupling processes in the thermosphere-ionosphere region. Most users of the data have focused on relative density variations. Scale differences between datasets and models have been largely neglected or removed using ad hoc scale factors. The origin of these scale differences arises from errors in the aerodynamic modelling, specifically in the modelling of the satellite outer surface geometry and of the gas-surface interactions. Therefore, the first step to remove the scale differences is to enhance the geometry modelling. This work forms the foundation for the future improvement of characterization of satellite aerodynamics and gas-surface interactions models at TU Delft, as well as for extending the use of sideways and angular accelerations in the aerodynamic analysis of accelerations and derivation of thermosphere datasets. Although work to improve geometry and aerodynamic force models by other authors has focused on CHAMP and GRACE, this paper includes the GOCE and Swarm satellites as well. In addition, it uses a density determination algorithm that is valid for arbitrary attitude orientations, enabling a validation making use of attitude manoeuvres. The results show an improvement in the consistency of density data between these four missions, and of data obtained before, during and after attitude manoeuvres of CHAMP and Swarm. The new models result in larger densities, compared to the previously used panel method. The largest average rescaling of density, by switching to the new geometry models is reached for Swarm at 32%, the smallest for GRACE at 5%. For CHAMP and GOCE, mean differences of 11% and 9% are obtained respectively. In this paper, an overview of the improvements and comparisons of data sets is provided together with an introduction to the next research phase on the gas-surface interactions.     

Novel active driven drop tower facility for microgravity experiments investigating production technologies on the example of substrate-free additive manufacturing

Through the striving of humanity into space, new production processes and technologies for the use under microgravity will be essential in the future. Production of objects in space demands for new processes, like additive manufacturing. This paper presents the concept and the realization for a new machine to investigate microgravity production processes on earth. The machine is based on linear long stator drives and a vacuum chamber carrying up to 1000?kg. For the first time high repetition rate and associated low experimental costs can provide basic research. The paper also introduces the substrate-free additive manufacturing as a future research topic and one of our primary application.     

重心位置对飞机阻力及其飞行性能的影响

为了降低配平状态下飞机的阻力问题,推导了飞机升致阻力与重心位置间的关系式。以一架典型的后平尾飞机为例。计算了向后移动飞机重心的位置,放宽对飞机固有静稳定度的要求对飞机配平升致阻力和总阻力以及对部分性能的影响。结果表明,当向后移动重心位置时,其配平升致阻力下降,并在某一重心位置时达最小值。     

三体随动跟踪式重力卫星姿态与无拖曳控制方法

采用非接触洛伦兹力执行器代替微推进系统,提出一种“质量块—载荷舱—平台舱”三体随动跟踪式重力卫星总体架构,避免传统低低跟踪重力场测量卫星设计中的质心波动与执行机构带来的动力学不确定性影响。其次,建立了该架构下的卫星姿轨耦合动力学模型,并在此基础上针对动力学非线性耦合项的影响,构建了一种基于带宽参数化自适应补偿的复合自抗扰控制方法,提升姿态与无拖曳控制性能。最后,采用数学仿真验证了所提出的重力卫星总体架构及其控制方法的有效性。仿真结果表明,该方法有效提升了系统的频域性能。     

凹腔结构对圆形超燃冲压发动机燃烧室阻力特性影响

凹腔作为促进燃烧室中燃料与来流混合和稳定燃烧的有效手段之一,其研究已引起人们的广泛关注.采用数值模拟方法,探索了圆形超燃冲压发动机燃烧室阻力特性随凹腔结构参数的变化趋势,同时初步考察了飞行攻角对凹腔阻力特性的影响.研究发现,凹腔摩阻相比压阻很小,凹腔时燃烧室的阻力特性主要体现在其压阻上;随着后掠角的增大,热试和冷流状态...     

考虑放宽静稳定度的民用客机气动优化设计

为了更加有效地减小民用客机考虑配平约束后的阻力,针对典型跨声速民用客机机翼-机身-平尾构型研究了不同静稳定度下的气动优化设计,并总结出在民用客机的减阻设计中考虑放宽静稳定度具有较大的减阻潜力。通过自由型面变形(FFD)技术对全机外形进行参数化,实现机翼型面的变形,进行气动优化设计并改变平尾的偏转保证全机能够力矩配平。采用基于雷诺平均Navier-Stokes(RANS)方程的离散伴随方法求解目标函数对设计变量的梯度,然后基于序列二次规划算法进行基于梯度的气动优化设计。基于CRM(Common Research Model)构型,针对不同参考重心位置进行了考虑配平约束的减阻优化设计研究,验证了优化设计系统的有效性,算例结果表明,随着重心位置后移即放宽静稳定度,优化构型配平阻力减小,外翼段前缘吸力峰值明显降低且双激波的强度得到有效减弱,此外机翼的升力系数分布更加贴合最佳升力系数分布。     

基于CFD的软式空中加油锥套气动特性研究

无人机空中加油缺少人为的观测与控制,若要进行自主控制下的空中加油,获取精准的气动数据则十分关键。基于CFD研究了国外某型锥套的气动特性,通过改变锥套支撑臂数量、空速以及稳定伞面积3个因素,构建了不同的三维子模型。利用数值计算分析了其对锥套气动参数的影响,并探究了影响规律。仿真结果表明,支撑臂数量和稳定伞面积均会影响阻力系数,而空速对阻力系数几乎没有影响。该方法可以用来预测影响因素发生变化时锥套阻力系数的变化趋势,为分析锥套气动特性提供了理论依据。     

沟槽面湍流减阻研究综述

对近20年来沟槽面湍流边界层特性、湍流拟序结构、湍流减阻及其机理的研究进展进行了综述.内容涉及沟槽面平板、旋成体、机翼等在压、跨、超音速流动情况下的实验研究成果;压力梯度、攻角、侧滑角等的影响;湍流猝发特性、紊动特性、近壁区带条结构的特征及减阻机理等方面的工作.为更有效地减少表面摩阻,必须深入开展对沟槽面湍流边界层特性、湍流拟序结构及湍流减阻机理等方面的研究.      

升力物体跨音速面积律

应用匹配渐近展开法推导出有升力物体的跨音速非线性面积律,给出升力效应当量源应满足的守恒条件及其确定方法。计算结果表明,对于~般飞机及其部件能较准确地估算其在跨音速流中零升力和有升力时的压差阻力,并可在飞机基本设计点状态下进行阻力优化而选择最佳构型。该方法延伸到低超音速情况亦具有足够准确度。计算方法简单、快速。     

叶片翼型结冰形态及其气动特性

针对风力机叶片翼型形状对结冰过程的影响及其导致的气动特性变化问题,采用欧拉法及热传质原理构建叶片结冰过程的数学模型并进行数值模拟分析。以NH02系列翼型族为例,建立翼型曲率特征模型,研究叶片关键参数如最大厚度对结冰量的影响机制,预测了某翼型在不同工况下的冰形及位置,探究了干净与结冰翼型的升、阻力特性变化规律。结果表明,结冰量与叶片的相对厚度及最大相对厚度所在位置呈正相关性;结冰导致升力系数变化范围为5%～20%,阻力系数为干净翼型的1.4～2.45倍;结冰致使翼型失速迎角变小,翼型提前进入失速状态。