双线圈高速开关阀的水击特性验证

高速开关阀是航天领域动力系统的关键元件,需要具备高频响和高可靠性。然而,高速开关阀的开关特性会使系统产生水击现象,降低系统的可靠性,尤其是在高速开关阀高频切换过程中会产生更多的水击压力波,致使系统中的水击变得更加复杂。因此,采用仿真和实验相结合的方法对不同频率下水击压力脉动的变化进行分析,最终通过对数据时域和频域的分析,发现了高速开关阀的水击压力脉动规律,研究结果可在航天动力系统中应用。     

空间双组元发动机离心式喷注器的喷注流场诊断技术研究

对空间双组元发动机核心部件喷注器的喷雾流场可视化诊断技术开展了研究,有效识别了传统分析手段难以发现的雾化场缺陷,对发动机工作特性进行早期诊断,实现故障预防和设计优化.离心式喷注器的雾化喷注流场包含了大量的数据信息,可以通过高速摄影和图像分析进行数据挖掘分析.通过均值图像和余弦相似性计算对喷注流场的空间分布结构进行诊断,...     

Nondestructive acquisition of the micro-mechanical properties of high-speed-dry milled micro-thin walled structures based on surface traits

Requirements for the service performance of aeronautic microelectronic components are increasingly strict. However, sever issues, that the acquisition of the service performance such as micro-mechanical properties is destructive, limit the subsequent application of the tested components. Addressing this issue, this paper proposes a nondestructive acquisition method of the micro-mechanical properties of the accelerometer micro-components, based on analyzing surface traits. To select qualified components without damage, we firstly developed a quasi-static micro-tensile tester and then established a combination prediction model of mechanical properties based on micro-milled surface traits. The model works due to the thin-walled structure, which makes the machined surface traits have significant influences on the mechanical properties such as Young’s modulus, yield strength, tensile strength, and elongation at break. Surface roughness, surface structure, and surface anisotropy are extracted to comprehensively present surface traits from different aspects. For improving the practicability of the model, the principal component analysis (PCA) is adopted to reduce high-dimensional traits explanatory variable space into two dimensions, and regression analysis models are comparative established in predicting the mechanical properties. Residuals analysis and error analysis are carried out to show the prediction accuracy. The maximum prediction error is about 10.62%, but the significance levels in the t-test of the predicted Young’s modulus and yield strength are not ideal. Therefore, kernel support vector regression (SVR) is imported to improve the prediction ability of the combination prediction model. The residuals analysis result shows that SVR is effective in enhancing the prediction ability of this model.     

Lean blowout characteristics of spray flame in a multi-swirl staged combustor under different fuel decreasing rates

Lean Blow Out(LBO) poses a significant safety hazard when occurring in aero-engines.Understanding the lower stability limits of gas turbine combustors and the characteristics of spray flame close to LBO are imperative for safe operation. The objective of this work is to evaluate the effects of fuel decreasing rates and pressure drops of the injector on LBO performances in a multiswirl staged combustor equipped with an airblast injector. A set of hardware and control system was developed to reali...     

Full mode flight dynamics modelling and control of stopped-rotor UAV

The Stopped-Rotor(SR) UAV combines the advantages of vertical take-off and landing of helicopter and high-speed cruise of fixed-wing aircraft. At the same time, it also has a unique aerodynamic layout, which leads to great differences in the control and aerodynamic characteristics of various flight modes, and brings great challenges to the flight dynamics modelling and control in full-mode flight. In this paper, the flight dynamics modelling and control method of SR UAV in full-mode flight is st...     

某高速着陆无人机方向舵纠偏控制设计及性能分析

无人机高速着陆过程中,由于侧风或初始干扰导致的滑跑侧偏极其危险。基于高速状态下方向舵纠偏效率高的特点,建立某无人机高速着陆动力学模型,设计方向舵纠偏控制策略,并基于Matlab/Simulink平台建立无人机滑跑非线性动力学模型及方向舵纠偏控制模型;对具有初始1°偏航角和1m/s持续垂直侧风情况下的无人机着陆工况进行仿真分析,并通过控制着陆速度、着陆初始姿态角和侧风强度,分析纠偏控制系统的性能。结果表明:所设计的纠偏控制系统具有一定的航向纠偏和抗持续侧风能力,最大侧偏距小于3 m,偏航角小于5°,较好地实现了高速滑跑阶段的侧向纠偏性能。     

Chatter stability and precision during high-speed ultrasonic vibration cutting of a thin-walled titanium cylinder

Titanium alloys are widely used in the aviation and aerospace industries due to their unique mechanical and physical properties. Specifically, thin-walled titanium (Ti) cylinders have received increasing attention for their applications as rocket engine casings, aircraft landing gear, and aero-engine hollow shaft due to their observed improvement in the thrust-to-weight ratio. However, the conventional cutting (CC) process is not appropriate for thin-walled Ti cylinders due to its low thermal conductivity, high strength, and low stiffness. Instead, high-speed ultrasonic vibration cutting (HUVC) assisted processing has recently proved highly effective for Ti-alloy machining. In this study, HUVC technology is employed to perform external turning of a thin-walled Ti cylinder, which represents a new application of HUVC. First, the kinematics, tool path, and dynamic cutting thickness of HUVC are evaluated. Second, the phenomenon of mode-coupling chatter is analyzed to determine the effects and mechanism of HUVC by establishing a critical cutting thickness model. HUVC can increase the critical cutting thickness and effectively reduce the average cutting force, thus reducing the energy intake of the system. Finally, comparison experiments are conducted between HUVC and CC processes. The results indicate that the diameter error rate is 10% or less for HUVC and 51% for the CC method due to a 40% reduction in the cutting force. In addition, higher machining precision and better surface roughness are achieved during thin-walled Ti cylinder manufacturing using HUVC.     

微波超宽带高速数控幅度调节器研制

微波频率源技术中常常要求实现微波输出信号功率电平的高精度、小步进调控。作为频率合成器中的重要组成部分, 微波功率幅度控制器的指标好坏对微波频率合成器的功率性能的优劣有很大影响。随着使用要求的不断提升，频率合成器等设备对带宽、速度的要求也越来越高。本文概述了微波超宽带高速幅度控制的背景及现状，详细介绍了微波超宽带高速数控幅度调节器设计原理、设计方法、实现手段及实现指标等内容。     

太阳风中的Alfven波耗散与电子和质子温度分布问题

根据动力论Alfven波耗散机制,详细计算了动力论Alfven波衰减的能量分配给质子和电子的比率.初步解释了高速太阳风中质子温度比电子温度高的事实,定性说明了r＜10R_s时电子快速冷却的原因.      

FAR29．785条款追踪分析

主要研究了美国民用航空规章（FAR）——运输类旋翼航空器适航标准第29．785条“座椅、卧铺、担架、安全带和肩带”的适航条款。首先研究了本条款的起源以及后来的发展历程，即历次修正案；同时分析了各次修正案修改的背景修改内容和修改原因。为航空器设计人员提高对航空器适航的认识提供了辅助性资料，使从事适航工作的人员能够更为准确地把握适航条款的本质目标，缩小与世界适航先进水平的差距。