强化处理对单晶叶片用氧化基陶瓷型芯的影响

对一种单晶叶片用的氧化铝基陶瓷型芯材料进行了特定的强化处理，研究其对型芯组织和性能的影响，发现强化后的陶瓷型芯体内形成了片状的莫来石晶全，其线膨胀峰值温度要比未经强化的型芯高出２００℃以上，高温性能得到了显著提高。     

钇铝石榴石对氧化铝基陶瓷型芯高温性能的影响

开发了一种钇溶胶为强化剂、通过真空压力浸渍强化处理改善氧化铝基陶瓷型芯高温性能的新工艺.研究了浸渍工艺对陶瓷型芯高温性能的影响,利用x射线衍射和SEM分析了陶瓷型芯相组成及其断口形貌.实验结果表明高温性能随着浸渍次数的增加而得到明显地改善.三次浸渍强化后,高温挠度从7.38 mm降低至0.72 mm,高温抗弯强度(15...     

相组成与微结构对硅基陶瓷型芯性能的影响

对比研究了A、B两种硅基陶瓷型芯的相组成与微结构及其对陶瓷型芯性能的影响.结果表明,B型陶瓷型芯的综合性能优于A型陶瓷型芯.     

定向空心叶片的陶瓷型芯

随着发动机叶片冷效的提高，用于制造空心叶片的陶瓷型芯必须承受结构复杂、工作条件苛刻的压力。本文着重阐述了几种用于定向空心叶片陶瓷型芯材料的组成、性能及成形工艺特点。     

淀粉对氧化铝基陶瓷型芯性能的影响

为了解决氧化铝基陶瓷型芯不易脱芯的难题,加入一定量的淀粉作为成孔剂。以白刚玉粉为基体材料、石蜡和蜂蜡为增塑剂、二氧化硅粉和氧化镁粉为矿化剂,采用热压注法制备氧化铝基陶瓷型芯;制备工艺参数如下：浆料温度为90℃、热压注压力为0.5 MPa、保压时间为25 s;研究不同淀粉加入量对氧化铝基陶瓷型芯性能的影响。结果表明：在烧结过程中,样品中淀粉的烧失,增大了氧化铝基陶瓷型芯内部的孔隙率;随着淀粉加入量的增加,氧化铝基陶瓷型芯的室温抗弯强度降低、显气孔率增大、溶失性增大、体积密度减小;经1560℃烧结2.5 h后,淀粉加入量为8%的氧化铝基陶瓷型芯综合性能最好,其室温抗弯强度为24.8 MPa、显气孔率为47.98%、溶失性为1.92 g/h、体积密度为1.88 g/cm3。     

矿化剂氧化铝的形貌对二氧化硅基陶瓷型芯性能的影响

制备了矿化剂为氧化铝的二氧化硅基陶瓷型芯,研究了矿化剂粉体粒径、形状等形貌特征对陶瓷型芯性能的影响。结果表明:随着氧化铝粉体粒径的增大,浆料流动性逐渐降低,加入氧化铝球形粉有利于改善浆料的充型性能;加入不规则形状氧化铝粉时,随着氧化铝粉体粒径的增大,型芯的烧结收缩率减小;加入球形氧化铝粉时,其粉体形状和粒径大小对收缩率和室温抗弯强度无明显影响,但导致较大的高温变形量。     

航空发动机叶片用陶瓷型芯的光固化增材制造研究现状

随着对高推重比和高效率航空发动机日益增长的需求,发动机叶片正朝着复杂空心结构的方向发展,而这对高性能复杂结构的陶瓷型芯提出了更高的要求.与此同时,基于光固化原理的增材制造技术可以实现无模具条件下的高精度、快速以及综合性能优异的陶瓷型芯制备.然而,目前基于光固化增材制造的陶瓷型芯制备工艺依旧面临控制尺寸精度、优化脱脂烧结...     

注射成型水溶性陶瓷型芯技术

水溶性陶瓷型芯对于内腔结构复杂和高尺寸精度的合金铸件的精密铸造成型起着十分关键的作用。本文系统介绍了近年来国内外水溶性陶瓷型芯注射成型技术的研究进展,并重点分析了对关键工艺过程如增塑剂制备、黏结剂和陶瓷粉体组分和粒径的选择、混料工艺优化、注射成型关键参数、脱脂烧结及防水处理等对型芯微观结构、质量和性能影响,为高性能水溶性陶瓷型芯的研制提供技术指导。最后,在总结现有技术特点的基础上,分析了未来水溶性陶瓷型芯注射成型技术的发展趋势,特别是新兴的纳米材料和技术以及计算机模拟技术,将为高性能和低成本型芯的研制提供必要的支持和保障。     

基于多种莫来石纤维的硅基陶瓷型芯增强机制及性能研究

分别以多晶、非晶莫来石纤维为增强相制备氧化硅基陶瓷型芯,探究纤维种类对型芯性能的影响。非晶纤维在促进方石英析晶、降低收缩率、提高气孔率方面的效果低于多晶纤维。相比于多晶纤维,非晶纤维具有较多结构缺陷,纤维与基体通过扩散传质形成紧密的结合,显著提高型芯的强度和抗蠕变性能,而且非晶纤维的亚稳态结构在碱性溶液中具有较高的化学活性,使型芯表现出优良的溶蚀性。非晶莫来石纤维质量分数为3%的硅基陶瓷型芯表现出优异的综合性能,其室温弯曲强度达27.7 MPa,高温弯曲强度为22.4 MPa,高温蠕变为0.31 mm,溶蚀率为1.26g/min,能够很好地满足空心叶片的浇注需求。     

工艺所推出陶瓷型芯模具和增力夹紧装置

工艺所推出陶瓷型芯模具和增力夹紧装置涡轮叶片陶瓷型芯模具制造技术和模具快速增力夹紧装置，已由北京航空工艺研究所研制成功并通过专家鉴定。这套制造技术完整、实用、成本低，符合工程化要求；快速增力夹紧装置结构新颖，操作简便，为陶瓷型芯制坯提供了新装备，可满...     

The effect of inlet conditions on the flow and heat transfer in multiple rotating cavity with axial throughflow

This paper discusses experimental results from two different build configurations of a heated multiple rotating cavity test rig.Measurements of heat transfer from the discs and tangential velocities are presented.The test rig is a 70% full scale version of a high pressure compressor stack of an axial gas turbine engine.Of particular interest are the internal cylindrical cavities formed by adjacent discs and the interaction of these with a central axial throughflow of cooling air.Tests were carried out for a range of non-dimensional parameters representative of high pressure compressor internal air system flows(Re up to 5×106 and Rez up to 2×105).Two different builds have been tested.The most significant difference between these two build configurations is the size of the annular gap between the(non-rotating) drive shaft and the bores of the discs.The heat transfer data were obtained from thermocouple measurements of surface temperature and a conduction solution method.The velocity measurements were made using a two component,LDA system.The heat transfer results from the discs show differences between the two builds.This is attributed to the wider annular gap allowing more of the throughflow to penetrate into the cavity.There are also significant differences between the radial distributions of tangential velocity in the two builds of the test rig.For the narrow annular gap,there is an increase of non-dimensional tangential velocity V/Ωr with radial location to solid body rotation V/Ωr=1.For the wider annular gap,the non-dimensional velocities show a decrease with radial location to solid body rotation.      

Research on Auto-detection for Remainder Particles of Aerospace Relay Based on Wavelet Analysis

Aerospace relay is one kind of electronic components which is used widely in national defense system and aerospace system. The existence of remainder particles induces the reliability declining, which has become a severe problem in the development of aerospace relay. Traditional particle impact noise detection (PIND) method for remainder detection is ineffective for small particles, due to its low precision and involvement of subjective factors. An auto-detection method for PIND output signals is proposed in this paper, which is based on direct wavelet de-noising (DWD), cross-correlation analysis (CCA) and homo-filtering (HF), the method enhances the affectiv-ity of PIND test about the small particles. In the end, some practical PIND output signals are analysed, and the validity of this new method is proved.     

Preparation of Highly Dispersed Antimony-doped Tin Oxide Nano-powder via Ion-exchange Hydrolysis of SnCl4 and SbCl3 and Azeotropic Drying

Antimony-doped tin hydroxide colloid precipitates have been synthesized by hydrolysis of SnCl4 and SbCl3 using: (1) an ion-exchange hydrolysis to remove chlorine ions, and (2) isoamyl acetate as an azeotropic solvent to obviate water. The obtained dried powder is of high dispersivity without any need for further grinding. The size and dispersivity of the final particles are investigated with the aid of TG-DTA, BET, XRD and TEM. After having calcined, the antimony-doped tin oxide nanopowder possesses a tetragonal rutile structure with high dispersivity, uniform particles and low hard agglomeration.     

Effects of Mo on the Microstructure and Hydrogen Sorption Properties of Ti-Mo Getters

The effects of Mo on the microstructure evolution, porosity and hydrogen sorption properties of Ti-Mo getters are investigated in this work. The results show that the addition of Mo prolongs the densification process of Ti-Mo getters and results in a significant amount of sintered pores. With the Mo content increasing, the porosity of getters firstly increases reaching the maximum value as it at- tains about 7.5wt.%, and then drops. At the room temperature, the hydrogen sorption property of getters increases progressively with the Mo content increasing, but the tendency is not very clear before its content lies below 2.5wt.%. When the Mo content achieves about 7.5wt.%, the hydrogen sorption property proves to be the best. The discussion is made about the above mentioned phenomena inclusive of hydrogen sorption properties of getters under different activation conditions (from 500-750 ℃).     

超声速燃烧数值模拟中的湍流与化学反应相互作用模型

高精度数值模拟有助于理解超声速湍流燃烧中湍流与化学反应的相互作用,可为发动机燃烧室等工程应用设计提供可靠的预测模型。除直接数值模拟外,目前在湍流燃烧应用中使用的大涡模拟和雷诺平均Navier-Stokes模拟均需要借助模型模化发生在湍流小尺度上的流动与化学反应过程对湍流大尺度运动的影响。现有的湍流与化学反应相互作用模型大致可分为:火焰面类模型和概率密度函数类模型,2类模型在不同的应用中各自具有优势和局限性。此外,现有模型大都基于低马赫数燃烧,而超声速燃烧中通常会伴随快速混合、局部熄火和再着火以及激波等复杂过程,这为发展其中的湍流与化学反应相互作用模型提出了更多的挑战。     

适于低轨卫星IP网络的单核共享树组播算法(英文)

为了解决低轨卫星IP网络中现有典型源组播算法的信道资源浪费问题,本文提出了一套单核共享树组播算法,即核心群合并共享树(CCST)和加权核心群合并共享树(w-CCST)算法。CCST 算法包括动态近似中心(DAC)选核方法和核心群合并组播路径构建方法。DAC方法专为周期、规律运动的低轨卫星网络提出,不需要复杂的星上计算。在核心群合并方法中,以核节点作为初始核心群,通过核心群和剩余组成员的最短路径方法逐步扩展直至整棵组播树构建完成,从而使得组播树的树代价最小,大大提高了网络的带宽利用率和组播传输效率。w-CCST 算法中所提出的加权因子可以调整树代价和端到端传播时延之间的折衷程度,因此,可以通过调整加权因子来适度增大树代价、降低端到端传播时延以支持某些端到端时延要求苛刻的实时组播业务。最后,与低轨卫星 IP 网络中典型算法进行了性能比较,仿真结果说明,CCST 算法的平均树代价比其它算法显著降低,w-CCST 算法的平均端到端传播时延小于 CCST 算法。     

Jet Vectoring Control Using a Novel Synthetic Jet Actuator

A primary air jet vectoring control system with a novel synthetic jet actuator (SJA) is presented and simulated numerically. The results show that, in comparison with an existing traditional synthetic jet actuator, which is able to perform the duty of either “push” or “pull”, one novel synthetic jet actuator can fulfill both “push” and “pull” functions to vector the primary jet by shifting a slide block inside it. Therefore, because the new actuator possesses greater efficiency, it has potentiality to replace the existing one in various appli- cations, such as thrust vectoring and the reduction of thermal signature. Moreover, as the novel actuator can fulfill those functions that the existing one can not, it may well be expected to popularize it into more flow control systems.     

Nonlinear Adaptive Slewing Motion Control of Spacecraft Truss Driven by Synchronous V-gimbaled CMG Precession

The slewing motion control of a truss arm driven by a V-gimbaled control-moment-gyro (CMG) is a nonlinear control problem. The V-gimbaled CMG consists of a pair of gyros that must precess synchronously. The moment of inertia of the system, the angular momentum of the gyros and the external disturbances are not exactly known. With the help of feedback linearization and recursive Lyapunov design method, an adaptive nonlinear controller is designed to deal with the unknown items. Performance of the proposed controller is verified by simulation.     

An SOR Implicit Time-accurate Scheme in Calculating Unsteady Flows

A new time-accurate marching scheme for unsteady flow calculations is proposed in the present work. This method is the combination of classical Successive Over-Relaxation (SOR) iteration method and Jacobian matrix diagonally dominant splitting method of LUSGS. One advantage of this algorithm is the second-order accuracy because of no factorization error. Another advantage is the low computational cost because the Jacobian matrices and fluxes are only calculated once in each physical time step. And, the SOR algorithm has better convergence property than Gauss-Seidel. To investigate its accuracy and convergency, several unsteady flow computa- tional tests are carried out by using the proposed SOR algorithm. Roe’s FDS scheme is used to discritize the inviscid flux terms. Un- steady computational results of SOR are compared with the experiment results and those of Gauss-Seidel. Results reveal that the numerical results agree well with the experimental data and the second-order accuracy can be obtained as the Gauss-Seidel for unsteady flow computations. The impact of SOR factor is investigated for unsteady computations by using different SOR factors in this algorithm to simulate each computational test. Different numbers of inner iterations are needed to converge to the same criterion for different SOR factors and optimal choice of SOR factor can improve the computational efficiency greatly.