Simulation and experimental investigation on a dynamic lateral flow mode in trepanning electrochemical machining

An appropriate flow mode of electrolyte has a positive effect on process efficiency, surface roughness, and machining accuracy in the electrochemical machining(ECM) process. In this study, a new dynamic lateral flow mode, in which the electrolyte flows from the leading edge to the trailing edge, was proposed in trepanning ECM of a diffuser. Then a numerical model of the channel was set up and simulated by using computational fluid dynamics software. The result showed that the distribution of the flow field was comparatively uniform in the inter-electrode gap. Furthermore, a fixture was designed to realize this new flow mode and then corresponding experiments were carried out. The experimental results illustrated that the feeding rate of the cathode reached 2 mm/min, the best taper angle was about 0.4°, and the best surface roughness was up to Ra= 0.115 lm. It reflects that this flow mode is suitable and effective, and can also be applied to machining other complex structures in trepanning ECM.     

Experimental study of hydrogen-rich/oxygen-rich gas-gas injectors

Five types of coaxial injectors were investigated experimentally using hot hydrogen-rich gas and oxygen-rich gas, which were respectively provided by a GH2/GO2 hydrogen-rich perburner and a GH2/GO2 oxygen-rich preburner. The injectors were the shear coaxial injector, the oxidizer post expansion coaxial injector, the fuel impinging coaxial injector, the central body coaxial injector, and the shear tri-coaxial injector. The characteristic velocity efficiency and the combustor＇s wall temperatures were obtained for different design parameters through the experiments. It can be con- cluded that angles of the oxidizer post expansion and the fuel impinging have little influence on the combustion performance and the wall temperatures. The contact area between fuel and oxidizer and the mass flow rate have significant impacts on the combustion performance. The shear tri-coaxial injector has the best combustion performance but also the highest wall temperatures among the five types of injectors.     

Experimental comparison between aircraft fuel tank inerting processes using NEA and MIG

Fuel tank inerting technologies are able to reduce the fire risk by injection of inert gas into the ullage or fuel, the former called ullage washing and the latter fuel scrubbing. The Green On-Board Inert Gas Generation System (GOBIGGS) is a novel technology based on flameless catalytic combustion, and owning to its simple structure and high inerting efficiency, it has received a lot of attentions. The inert gas in the GOBIGGS is mainly comprised of CO₂, N₂, and O₂ (hereinafter, Mixed Inert Gas (MIG)), while that in the On-Board Inert Gas Generation System (OBIGGS), which is one of the most widely used fuel tank inerting technologies, is Nitrogen-Enriched Air (NEA). The solubility of CO₂ is nearly 20 times higher than that of N₂ in jet fuels, so the inerting capability and performance are definitely disparate if the inert gas is selected as NEA or MIG. An inerting test bench was constructed to compare the inerting capabilities between NEA and MIG. Experimental results reveal that, if ullage washing is adopted, the variations of oxygen concentrations on the ullage and in the fuel are nearly identical no matter the inert gas is NEA or MIG. However, the ullage and dissolved oxygen concentrations of MIG scrubbing are always higher than those of NEA scrubbing.     

飞机数字化设计数模发放控制

数字化产品和过程模型、产品信息管理、高性能计算、以及数据传输，已经成为飞机型号研制中的重要技术手段。结合数字化技术在飞机型号研制中的实际应用，探讨了设计数据模型发放过程控制，包括发放原则、发放流程、数据文件准备和发放审签等，对数据模型的审签过程控制内容做了详细的论述；介绍了数据模型成熟度以及数据文件的存储、获取和归档管理。     

冶金法提纯多晶硅退火工艺优化的数学模型分析与试验验证

冶金法制备多晶硅过程中,通过对不同退火温控方案进行数学建模,探求优化的退火理论温度控制函数与曲线。数学模型表明,对硅铸锭直接进行保温,依靠自然热平衡退火,会使内部应力大于产生位错的临界应力;采用加热元件对硅铸锭适当加热保温可减缓降温速率。通过比较,选择较低的退火温度1 236℃和较短的退火时间8.52 ks作为试验退火温控方案。试验验证表明,该退火方案得到的多晶硅铸锭目视裂纹较少,少数载流子寿命与电阻率具有明显优势。     

基于DOE优化湍流模型的SERN分离点预测数值模拟与实验验证

在SERN(Simple expansion ramp nozzle)中,流动分离现象伴随着激波/边界层相互干扰、强剪切层、强激波等复杂的流动现象,导致通用的计算流体力学软件对SERN中分离点、分离区和再附点的计算精度不能满足工程需要。为了提高SERN中分离点的计算精度,基于Allamaprabhu等的研究成果,针对Menter的SST(Shear stress transport)模型,将修改湍流模型经验参数的方法运用到SERN分离流动的预测中,并利用试验设计(Design of experiment,DOE)优化方法得到了经验参数的最优组合,使计算和实验的无量纲分离点和无量纲分离点压力的误差分别降至1.99%,4.38%,压力分布均方根误差降至7.83%。     

A numerical model for bird strike on sidewall structure of an aircraft nose

In order to examine the potential of using the coupled smooth particles hydrodynamic(SPH) and finite element(FE) method to predict the dynamic responses of aircraft structures in bird strike events, bird-strike tests on the sidewall structure of an aircraft nose are carried out and numerically simulated. The bird is modeled with SPH and described by the Murnaghan equation of state, while the structure is modeled with finite elements. A coupled SPH–FE method is developed to simulate the bird-strike tests and a numerical model is established using a commercial software PAM-CRASH. The bird model shows no signs of instability and correctly modeled the break-up of the bird into particles. Finally the dynamic response such as strains in the skin is simulated and compared with test results, and the simulated deformation and fracture process of the sidewall structure is compared with images recorded by a high speed camera. Good agreement between the simulation results and test data indicates that the coupled SPH–FE method can provide a very powerful tool in predicting the dynamic responses of aircraft structures in events of bird strike.     

飞机燃油氧气析出计算方法研究

为降低燃油箱发生爆炸的风险,需在油箱中设置抑爆系统。咨询通告规定,要计算燃油箱平均氧气浓度,需考虑燃油中的氧气析出。根据不同高度下空气在燃油中的溶解度平衡关系及空气中氧氮分压关系,得m飞机随飞行高度变化氧气析出的计算方法。     

Thermal performance of a 3D printed lattice-structure heat sink packaging phase change material

Thermal storage technology is becoming more and more significant with the increase of high-power equipment in space applications. In this paper, 3D printing technology and Phase Change Material (PCM) were combined into a Thermal Energy Storage (TES) system, which could fulfill the requirements of light weight and high thermal conductivity. A 3D-printed lattice-structure TES plate with N-tetradecane as the PCM and aluminum alloy as the thermal conductivity enhancer was manufactured, and experimentally tested in a thermal vacuum chamber. In addition, a simplified simulation model of the lattice cell was established to clearly analyze the heat transfer process of the TES plate. The effects of initial temperature distribution and heat load gradient on the thermal storage performances were investigated experimentally and theoretically. The equivalent thermal conductivity of the 3D-printed lattice-structure TES plate turns out to be 13 times of the pure PCM thanks to the aluminum skeleton. The heat transfer enhancement appears at the end of the phase change stage due to the sudden mixture of the PCM with different temperature. The simulation results agree well with the experimental data. The equivalent thermal conductivity obtained by the phase change simulations are a little higher than those of the experiments, which is mainly caused by the initial uneven temperature distribution in the tests. Additionally, the effects of non-uniform heat load and the presence of the PCM in the TES plate are studied. This work successfully validates the feasibility and effectiveness of 3D printing technology and TES technology for the temperature control in space applications.