2相多循环脉冲爆震发动机燃烧噪声辐射特性试验研究

对内径为60 mm的2相多循环脉冲爆震发动机燃烧噪声辐射特性,在其测量位置处和一定试验频率范围内进行了试验研究。经研究发现:在一定低频范围内,噪声辐射频谱由气流脉冲的基频(即爆震频率)和谐频组成;脉冲噪声是1个或多个持续时间小于1s的猝发声组成的噪声;距离发动机喷口方向越近,噪声的声压级越强;反之,噪声衰减的速度越快。     

半埋入式S弯进气道主动流动控制研究

为了改善半埋入式亚声速S弯进气道出口气流品质,本文采用吹、吸气方式对其进行了主动流动控制数值研究。结果表明:吸气位置、吸气量变化显著影响进气道气动性能,最佳吸气位置位于唇口附近,当唇口吸气量为进气道流量的1.9%时,总压畸变指数降低约45.7%,总压恢复系数和增压比略有提高;而附面层吹气时进气道的性能仅在吹气量较小时有所改善;附面层吹、吸组合控制对流场的改善程度介于上述方案之间,而非单独吹、吸气方案效果的简单叠加。     

Investigation of straightforward impedance eduction method on single-degree-of-freedom acoustic liners

In order to address the current aircraft noise problem, the knowledge of impedance of acoustic liners subjected to high-intensity sound and grazing flow is of crucial importance to the design of high-efficiency acoustic nacelles. To this end, the present study is twofold. Firstly, the StraightForward impedance eduction Method (SFM) is evaluated by the strategy that the impedance of a liner specimen is firstly experimentally educed on a flow duct using the SFM, and then its accuracy is checked by comparing the numerical prediction with the measured wall sound pressure of the flow duct. Secondly, the effects of grazing flow and high-intensity sound on the impedance behavior of two single-layer liners are investigated based on comparisons between educed impedance and predictions by three impedance models. The performance of the SFM is validated by showing that the educed impedance leads to excellent agreement between the simulation and the measured wall sound pressure for different grazing flow Mach numbers and Sound Pressure Levels (SPLs) and over a frequency range from 3000?Hz down to 500?Hz. The grazing flow effect generally has the tendency that the acoustic resistance exhibits a slight decrease before it increases linearly with an increase in Mach, predicted successfully by the sound-vortex interaction theoretical model and the Kooi semi-empirical impedance model. However, the Goodrich semi-empirical impedance model gives only a simple linear relation of acoustic resistance starting from Mach zero. Additionally, when the SPL increases from 110 to 140?dB in the present investigation, the acoustic resistance exhibits a significant increase at all frequencies in the absence of flow; however, the resistance decreases slightly under a grazing flow of Mach 0.117. It indicates that the SPL effect can be greatly inhibited when flow is present, and the grazing flow effect can be reduced partly as well at a relatively high SPL.     

Impact of aperture on dynamic response of sandwich plates with aluminium face-sheets and PMI core based on an alternative finite element formulation and experiments

Apertures generally exist in the sandwich structures attributing to mechanical connection and lightweight, which might induce failure of such structures. Thus, it is required to realize the impact of aperture on mechanical behaviors of sandwich structures. If transverse shear deformations are unable to be described accurately, the reasonable prediction of dynamic behaviors of the form-core sandwich plates with apertures will meet severe challenges due to a large difference of transverse shear mo...     

Experimental investigation of shock-buffet criteria on a pitching airfoil

An experimental investigation of the shock-buffet phenomenon subject to unsteady pitching supercritical airfoil around its quarter chord has been conducted in a transonic wind tunnel. The model was equipped with pressure taps connected to the fast response pressuretransducers. Measurements were conducted at different free-stream Mach number from 0.61 to0.76. The principle goal of this investigation was to experimentally discuss the shock-buffet criterion over a SC(2)-0410 supercritical pitching ...     

Refined modeling and experimental verification of a torque motor for an electro-hydraulic servo valve

The Permanent Magnet Torque Motor (PMTM) is the key electro-mechanical conversion device in an Electro-Hydraulic Servo Valve (EHSV). In this work, a refined model of a PMTM is developed, considering the non-working air-gaps between the upper or lower yoke and the armature, the fringing effect at the limiting holes, and the nonlinear permeability of soft magnetic material. Based on the refined model, the influences of various factors on the calculation accuracy of the magnetic flux at the pole surfaces of the armature and the output torque are investigated. For verifying the validity of the refined model, a Finite Element Analysis (FEA) of the PMTM is conducted, and a test platform is constructed. Compared with existing models, the refined model can better reveal the intrinsic mechanism of the PMTM, and its calculations are more consistent with the FEA results. The experimental results of the armature deflection displacement show that the refined model can accurately describe the output characteristics of the PMTM.     

无人机滑跑侧翻现象建模与控制设计

无人机的安全滑跑是整个飞行任务的基础,也是其重复使用的重要前提.以前三点式无人机为研究对象,重点研究了滑跑阶段的安全保护策略以及航向保持控制律.首先对滑跑过程中最常见的侧翻现象进行建模,并通过侧翻试验验证了模型的正确性.然后基于侧翻模型提出了预防侧翻的安全边界,并设计了侧翻保护系统.其次,通过试验辨识出前轮转角对航向角...     

某扭力管万向节组件及支撑轴承的正弦振动疲劳研究

本文建立C919某扭力管万向节组件及支撑轴承的有限元模型，对其进行模态分析及正弦分析，推导了正弦振动下的疲劳寿命计算公式并预估了模型的寿命，通过模态试验验证了模型的正确性，通过正弦试验验证了疲劳寿命计算的正确性。该疲劳寿命计算方法可用来预估相关模型的正弦振动疲劳寿命。     

Influence and experiment of cable-net manufacturing errors on surface accuracy of mesh reflector antennas

Cable-net structures are of substantial importance in the construction of large mesh reflector antennas. Owing to the inevitable errors in their manufacturing process, the reflector surface accuracy deteriorates. This study makes a comprehensive investigation of random manufacturing errors during constructing the mesh reflector antennas, and analyze its influence on reflector surface accuracy. Firstly, the sensitivity of reflector surface accuracy with respect to the random errors of the unstressed cable length is mathematically deducted. Secondly, a non-button connecting method is proposed and analyzed to reduce manufacturing errors. Thirdly, two physical experiment models based on 2.62-meter mesh reflector antenna are made. Finally, numerical examples and experimental tests are given to demonstrate the effectiveness of the proposed method. Compared with the traditional method, the proposed method can effectively reduce the influence of the manufacturing errors on the reflector surface accuracy. Moreover, the reduction in the sizes of the nodes also reduces the risk of entanglement of the mesh reflector antenna during the deployment process, and thereby improves the deployment reliability.     

Investigation of pressure wave behaviors in the rotational speed effects on a pressure-exchange wave rotor

A wave rotor is suitable for compact and efficient pressure-exchange between gas flows.This work measured the circumferential pressure distribution of the rotor/stator interfaces and utilized a CFD method to simulate the unsteady pressure waves. The experimental and CFD results showed some slopes in the circumferential pressure distributions, and the slopes indicated the traces of specific unsteady pressure waves. Such traces varied regularly if the rotational speed varied within a range from-11...