一种用于土卫六探测的热机浮空器性能分析

针对土卫六大气环境的特点,提出利用大气温度梯度发电的热机浮空器解决探测器能源问题。介绍该热机浮空器的系统组成和基本工作原理,分析应用于土卫六探测的可行性和发电性能。结果表明热机浮空器能够将土卫六低品位的大气热能转换为电能;涡轮机喷管喉部的半径和飞行高度等设计参数对热机的性能有较大的影响。     

Modified robust optimal adaptive control for flight environment simulation system with heat transfer uncertainty

To solve the rapid transient control problem of Flight Environment Simulation System (FESS) of Altitude Ground Test Facilities (AGTF) with large heat transfer uncertainty and disturbance, a new adaptive control structure of modified robust optimal adaptive control is presented. The mathematic modeling of FESS is given and the influence of heat transfer is analyzed through energy view. To consider the influence of heat transfer in controller design, we introduce a matched uncertainty that represents heat transfer influence in the linearized system of FESS. Based on this linear system, we deduce the design of modified robust optimal adaptive control law in a general way. Meanwhile, the robust stability of the modified robust optimal adaptive control law is proved through using Lyapunov stability theory. Then, a typical aero-engine test condition with Mach Dash and Zoom-Climb is used to verify the effectiveness of the devised adaptive controller. The simulation results show that the designed controller has servo tracking and disturbance rejection performance under heat transfer uncertainty and disturbance; the relative steady-state and dynamic errors of pressure and temperature are both smaller than 1% and 0.2% respectively. Furthermore, the influence of the modification parameter γ is analyzed through simulation. Finally, comparing with the standard ideal model reference adaptive controller, the modified robust optimal adaptive controller obviously provides better control performance than the ideal model reference adaptive controller does.     

面向空间应用的单向微膨胀型热开关特性分析

为了提高探测器等航天器的温度控制精度,降低热波动造成的影响,基于金属的热胀冷缩原理设计了一种单向膨胀型热开关,利用二维稳态导热原理进行建模分析,得到热开关热特性参数。搭建了试验平台模拟热开关工作环境,测定不同功率条件下热开关的工作状态以及相关性能参数。当加热功率为04W时开关断开热阻为23046K/W;功率为30W时开关的导通热阻为03022K/W,开关控制比为7626。结果表明,试验数据与理论计算数据吻合较好,进一步说明了热开关的结构合理性以及适用性。     

微重力条件下热管吸热器瞬态热分析

基于微重力条件下的导热控制微分方程,采用焓法对热管吸热器相变材料容器进行了二维数值建模与仿真,在同时考虑空穴和相变的情况下,对微重力条件下蓄热单元相变传热进行了模拟计算,分析了空穴率对蓄热容器内部的温度场和热性能的影响,并将计算结果同美国航空航天局（NASA）方案热管吸热器蓄热单元相变传热计算结果进行了比较,验证了文中微重力条件下计算模型的合理性与准确性。研究结果表明：空穴影响着蓄热单元相变的进程,空穴的存在增加了容器内部的温度梯度,使得容器的蓄热能力降低;由于热管径向温差较小,热管壁温在相变材料熔点附近变化较小,从而在一定程度上能缓解热斑和热松脱现象。     

前缘射流对涡轮导叶吸力面多排气膜孔冷却特性的影响

为了研究前缘射流对吸力面多排气膜孔下游冷却特性的影响,在跨声速风洞中进行了实验并采用热电偶获得了气膜冷却效率和换热系数。叶栅进口雷诺数的范围为2.0×105 ~ 4.0×105,出口等熵马赫数为0.95,叶栅前的湍流度小于5%。前缘布置6排对冲圆柱孔,质量流量比的范围为2.00% ~ 3.71%,吸力面布置4排圆柱孔,质量流量比的范围为2.02% ~ 3.74%。实验结果表明：在没有前缘射流时,吸力面的气膜冷却效率随质量流量比增大先升高后下降,存在前缘射流时,质量流量比对气膜冷却效率的影响较小。对所有的工况而言,质量流量比增大都提高了吸力面的换热系数。相比于没有前缘射流的工况,前缘射流显著提高了吸力面孔排附近区域的气膜冷却效率并略微降低了换热系数;在吸力面后半段,前缘射流显著提高了换热系数而对气膜冷却效率影响较小。总的来说,前缘射流改善了吸力面孔排附近区域的冷却效果,但是恶化了吸力面后半段区域的冷却效果。     

浮升力对竖直上升圆管内超临界航空煤油换热的影响及评价准则

为深入理解航空发动机再生冷却热防护中的换热机理,对竖直上升圆管内超临界压力RP-3航空煤油的传热恶化开展了实验研究。探究了两类传热恶化的换热特征和形成机理,考察了热流密度、质量流量和进口压力对传热恶化的影响机制。获得了两类传热恶化的起始条件判别准则。以Nu/Nu0=0.75作为依据,建立了浮升力影响评价准则。通过格拉晓夫数修正实现了换热关联式预测。结果表明：两类传热恶化出现在不同条件下,低温区传热恶化源于边界层转捩和浮升力的综合作用,当进口雷诺数高于5730时其不再出现;高温区传热恶化的临界热流密度可以表述为质量流量的函数关系。当浮升力参数Grb/Re2.7和Gr/Re2分别高于10-7、10-3时,浮升力作用不可忽略。改进的换热关联式具有合理的预测精度,满足热防护系统设计的工程运用。     

Whole-process modeling of titanium disc forming for gradient distributions of temperature and deformation

Gradient distributions of temperature and deformation (GDTD) are crucial for achieving dual-performance discs of titanium alloys which is required by the service environment of aeroengine. However, heating, cooling and deforming sequence in the whole process of the titanium disc forming, which leads to difficulties for achieving GDTD due to a lot of parameters. To solve this problem, a whole-process model of the titanium disc forming for GDTD has been established. In the model, heating and cooling via heat radiation, conduction and convection, and deforming by local loading with mold chilling are all considered. Experiments on heating and cooling as well as deforming were carried out by using a furnace and the Gleeble-3500 machine. The experimental data are used to determine thermal parameters and constitutive relations of the IMI834 titanium alloy, and then to verify the reliability of the model. Then the model was used to simulate the evolution rules of temperature and deformation of the titanium disc. The results show that the heating surface, furnace temperature, billet profile and loading rate play the core role for the control of GDTD, and thus a set of parameters were determined. Therefore, this work provides a base for developing a new forming technology of the dual-performance titanium discs with the approach of local heating and local loading.     

Numerical simulation of compression corner flows at Mach number 9

A hypersonic vehicle encounters a wide range of conditions during its complete flight regime. These flight conditions may vary from low to high Mach numbers with varying angles of attack. The near-wall viscous dissipation associated with flows at combined high Mach and Reynolds numbers leads to significant wall heat transfer rates and shear stresses. The shock wave/boundary-layer interaction results in a flow separation region, which commonly augments total pressure losses in the flow and lowers the efficiency of aerodynamic control surfaces such as fins installed on a vehicle. The standard turbulence models, when used to resolve such flows, result in incorrect separation bubble size for large separated flows. Therefore, it results in an inaccurate aerodynamic load, such as the wall pressures, skin friction distribution, and heat transfer rate. In previous studies, the application of the shock-unsteadiness correction to the standard two-equation k-ω turbulence model improved the separation bubble size leading to an accurate pressure prediction and shock definition with the assumption of constant Prandtl number. In the present work, the new shock-unsteadiness modification to the k-ω turbulence model is applied to the hypersonic compression corner flows. This new model with variable Prandtl number is based on the model parameter, which depends upon the local density ratio. The computed wall pressures, heat flux and flow field are compared to the experimental data. A parametric study is carried out by varying compression deflection angles, free stream Reynolds number and wall temperatures to compute the flow field and wall data accurately, particularly in the shock boundary layer interaction region. The new shock-unsteadiness modified k-ω model with variable Prandtl number shows an accurate prediction of initial pressure rise location, pressure distribution in the plateau region and heat flux in comparison to the standard k-ω model.     

耦合CFD径向微动分析的航空齿轮泵轴承起动瞬时润滑特性研究

为研究处于动态起动过程中航空齿轮泵齿轮轴-轴瓦隙内油膜的润滑问题,在齿轮泵CFD仿真模拟的基础上,基于齿轮轴所受载荷与轴承间隙起动混合支撑作用的动力学关系,实现了耦合CFD的轴心径向微动分析。对处于齿轮泵瞬态场影响下的滑动轴承起动瞬时润滑特性及接触行为进行了数值分析。仿真结果表明:齿轮泵瞬态场变化产生的载荷波动对轴心微动产生的影响在起动低偏心阶段更为明显,造成的最终静平衡位置在不同方向上差异为0.43%和7.29%;润滑界面微观粗糙度的影响存在于起动高偏心阶段;在泵进口压力不变的条件下,其出口压力的增大不改变固体接触力的作用时间,但会使接触现象加剧;齿轮泵稳定工作转速的增大会减小接触作用时间,并且使不同方向接触力的差值减小;齿轮泵工况改变对于最小油膜厚度的影响相似于轴心轨迹,当出口压由3.02MPa增至9.1MPa时,最小膜厚减小率最大可达26.32%和101.43%。     

A refined design method for precoolers with consideration of multi-parameter variations based on low-dimensional analysis

The precooler is a distinctive component of precooled air-breathing engines but constitutes a challenge to conventional thermal design methods. The latter are based upon assumptions that often reveal to be limited for precooler design. In this paper, a refined design method considering the variations of fluid thermophysical properties, flow area and thermal parameters distortion,was proposed to remediate their limitations. Firstly, the precooler was discretized into a fixed number of sub-microtu...