Mixing and combustion characteristics in a scramjet combustor with different distances between cavity and backward-facing step

The mixing and combustion characteristics in a cavity flameholding combustor under inlet Mach number 2.92 are numerically investigated with ethylene injection. Dimensionless distance is defined as the ratio of the actual distance to the height of the combustor entrance. The cavity shear-layer mode, the lifted cavity shear-layer mode, and jet wake mode with upstream separation are observed respectively with dimensionless distance equals to 1.5, 4.5, and 7.5. In both non-reacting and reacting flow...     

Promotional effect of silica on the combustion of nano-sized aluminum powder in carbon dioxide

This paper presents how the combustion performance of nano-sized aluminum(nAl)powder in carbon dioxide are affected by silica. The ignition and combustion performance of nAl powder with silica addition were studied by a high-temperature tube furnace. An s-type thermocouple and a high-speed motion acquisition instrument were performed to evaluate the ignition temperature, maximum combustion temperature, maximum change of rate of temperature, and combustion propagation speed. The combustion effici...     

Passive attitude stabilization of ionic-wind-powered micro air vehicles

The ionic-wind-powered Micro Air Vehicles (MAVs) can achieve a higher thrust-to-weight ratio than other MAVs. However, this kind of MAV has not yet achieved controlled flight because of the unstable thrust produced by the ionic wind and the dynamic instability related to the small size. In this paper, a passive attitude stabilization method of the ionic-wind-powered MAV using air dampers is introduced. The key factors that influence the performance of the air dampers, including the layout, position, and area of the air dampers, are theoretically studied. The appropriate optimal position of the air dampers is also obtained by Monte Carlo stochastic simulations. Then the proposed passive attitude stabilization method is applied to the ionic-wind-powered MAVs of different wingspan (2 cm and 6.3 cm). Finally, the experimental results show that using the proposed method, attitude stabilization is achieved for the first time for the ionic-wind-powered MAV. Moreover, the altitude control of an ionic-wind-powered MAV with a wingspan of 6.3 cm is also demonstrated.     

Numerical investigation on leakage and rotordynamic performance of the honeycomb seal with swirl-reverse rings

Honeycomb seals are a crucial component to restrict the leakage flow and improve system stability for the turbomachines and aero-engines. In this work, the leakage and rotordynamic performance of honeycomb seals with the Swirl-Reverse Ring(SRR) is predicted by employing the approach of Computational Fluid Dynamics(CFD) and the multifrequency whirling model theory.Numerical results show that the positive preswirl flow and circumferential velocity can be effectively weakened for the honeycomb seal...     

天梯动力学与控制研究进展

简要介绍了天梯系统的组成和初始部署形式。在此基础上，针对天梯初始部署和运行中存在的复杂动力学与控制问题，分别从天梯动力学建模、天梯稳定性、天梯绳索振荡、攀爬器运动引起的绳索振荡及振荡抑制、天梯初始部署动力学五个方面分析归纳了天梯动力学与控制的发展状况，最后对天梯动力学与控制的发展方向进行了总结及展望。     

高精度星间测距与超稳振荡器研究

高精度K频段微波星间测距系统（KBR）采用双路微波测距技术,测量精度可达到1μm／s,是地球重力场测量卫星的三大有效载荷之一。作为整个系统时间基准的超稳定振荡器（USO）,是实现KBR微米级测量精度的关键。文章在研究KBR测距技术的基础上,对USO进行了研究和设计,研制成功的USO的短期频率稳定度达到了5×10^-13／s（Allan方差）,达到了指标要求。     

Numerical study on combustion efficiency of aluminum particles in solid rocket motor

The combustion of aluminum particles in solid rocket motor plays an important role in energy release of propellants. However, due to the limited residence time, aluminum particles may not be burned completely, thus hindering the improvement of specific impulse. This study aims to explore the characteristics of aluminum combustion efficiency and its influencing factors by experiments and numerical simulations, providing a guideline for engine performance improvement. As an input of simulation, the initial agglomerate size was measured by a high pressure system. Meanwhile, the size distribution of the particles in plume was measured by ground firing test to validate the numerical model. Then, a two-phase flow model coupling combustion of micro aluminum particle was developed, by which the detailed effects of particle size, detaching position and nozzle convergent section structure on aluminum combustion efficiency were explored. The results suggest that the average combustion temperature in the chamber drops with increasing initial particle size, while the maximum temperature increases slightly. In the tested motors, the aluminum particle burns completely as its diameter is smaller than 50 μm, and beyond 50 μm the combustion efficiency decreases obviously with the increase of initial size. As the diameter approaches to 75 μm, the combustion efficiency becomes more sensitive to particle size. The combustion efficiency of aluminum particle escaping from end-burning surfaces is significantly higher than that from internal burning surface, where the particle combustion efficiency decreases during approaching the convergent section. Furthermore, the combustion efficiency decreases slightly with increasing nozzle convergent section angle. And theoretically it is feasible to improve combustion efficiency of aluminum particles by designing the convergent profile of nozzle.     

跨声速压气机叶片掠和机匣处理组合效应的机理研究

针对典型跨声速压气机转子，采用非定常数值模拟方法研究了叶片掠设计和机匣处理的组合作用对压气机转子性能的综合影响。分别探讨了转子前掠、后掠和掠叶片与机匣处理组合等形式对转子峰值效率和稳定工作裕度的影响效果和内在机制。研究发现，前掠转子与机匣处理组合能够以较小的效率损失（-0.56%）为代价获得最佳的扩稳效果；在前掠转子与机匣处理组合作用下，对间隙泄漏流的动量激励和叶顶低能堵塞流体的有效消除是组合机匣处理扩稳的本质原因。结果表明，采取前掠转子和机匣处理的组合形式，可以弥补前掠转子设计损失转子最大负荷的不足，同时以较少的效率损失代价充分发挥了机匣处理的扩稳潜力。