Numerical investigation on unsteady characteristics of ducted fans in ground effect

Ducted fans are widely used in various applications of Unmanned Aerial Vehicles(UAVs) due to the high efficiency, low noise and high safety. The unsteady characteristics of ducted fans flying near the ground are significant, which may bring stability problems. In this paper, the sliding mesh technology is applied and the Unsteady Reynolds Averaged Navier-Stokes(URANS)method is adopted to evaluate the influence of ground on the aerodynamic performance of ducted fans. The time-averaged results sho...     

Accelerated initiation of oblique detonation induced by disturbance in detonative zone

In the real flow for high altitude, the initiation mechanism of the oblique detonation involves the coupling of complex wave structures and combustion waves, which may result in the phenomenon of extinction. The approach of stable initiation is one of the key factors that restricting the oblique detonation engine from theory to practice. The wave structure, initiation characteristics and characteristic parameters of the flow field are analyzed, the two-dimensional Euler equation considering the ...     

Breakthrough detection in electrochemical discharge drilling to enhance machining stability

Film cooling holes are widely used in aero-engine turbine blades. These blades feature large numbers of holes with complex angles and require a high level of surface integrity. Electrochemical discharge drilling(ECDD) combines the high efficiency of electrical discharge drilling(EDD) with high quality of electrochemical drilling(ECD). However, due to the existence of a variety of energy for material removal, accurate and timely detection of breakthroughs is fraught with difficulties. An insuffic...     

Study on the Deformation Behavior of Mg-Gd-Y-Zn-Mn Wrought Magnesium Alloys by Visco-plastic Self-consistent Modeling

The plastic deformation behavior of new Mg-Gd-Y-Zn-Mn magnesium alloys gains great necessity to clarify and understand the mechanism deeply. In the present work， the tensile mechanical property test and visco-plastic self-consistent (VPSC) model are used to investigate the activities of deformation modes of VW84M and VW94M magnesium alloys during the tensile deformation. The results show that the mechanical properties of the above extruded alloys are similar but VW94M has higher strength than VW84M after the same aging process. Compared with the extruded alloys， the as-aged alloys have significantly higher activation of pyramidal slip at the later stage of plastic deformation. In addition， the as-aged VW94M alloy with higher strength has the largest activity of pyramidal slip. In summary， the addition of Gd increases the critical resolved shear stress (CRSS) in each slip system of VW94M， while the increase in the strength and the decrease in the elongation of as-aged alloys are associated with the significant activation of pyramidal slip.     

Analysis of grinding mechanics and improved grinding force model based on randomized grain geometric characteristics

Too high grinding force will lead to a large increase in specific grinding energy, resulting in high temperature in grinding zone, especially for the aerospace difficult cutting metal materials,seriously affecting the surface quality and accuracy. At present, the theoretical models of grinding force are mostly based on the assumption of uniform or simplified morphological characteristics of grains, which is inconsistent with the actual grains. Especially for non-engineering grinding wheel,most g...     

一种用于TSTO级间分离CFD计算的网格动态优化技术

两级入轨空天运输系统具有难度较低和经济性好的优点，级间分离是该运输系统设计的一项关键技术。相比前后串联级间分离，两级入轨上下两级间存在严重的激波相互干扰，直接影响分离物体的气动力矩。为了更好地模拟分离过程中两级之间的运动激波多次反射问题，本文结合非结构混合网格分布优化技术和压力比值激波识别技术，建立了用于级间分离运动过程的并行网格动态优化技术。基于计算流体力学软件NNW-FlowStar，完成了两级入轨运输系统并联分离过程的数值模拟。结果表明，采用网格动态优化技术，可实现级间复杂激波的精细捕捉，更精准地获得了强干扰下飞行器的气动特性，显著提高了并联分离过程中运动轨迹和姿态的预测精度。     

Experimental investigation on unstart-restart hysteresis of a supersonic inlet during throat regulation

The hysteresis during the throat regulation process of a supersonic variable inlet is unconducive to restart. Hence, detailed experimental studies of such a hysteresis and its control are necessary. A throat variable supersonic inlet was designed at a shock-on-lip Mach number of4.0 and an Internal Contraction Ratio(ICR) ranging over 1.21–2.94. Meanwhile, a distributed bleed system was proposed to suppress the hysteresis. The wind tunnel tests were conducted at Mach number 2.9. The throat regulat...     

Transition control of a tail-sitter unmanned aerial vehicle with L1 neural network adaptive control

The main task of this work is to design a control system for a small tail-sitter Unmanned Aerial Vehicle(UAV) during the transition process. Although reasonable control performance can be obtained through a well-tuned single PID or cascade PID control architecture under nominal conditions, large or fast time-varying disturbances and a wide range of changes in the equilibrium point bring nonlinear characteristics to the transition control during the transition process, which leads to control prec...     

Plasma transport simulation under different conditions and optimization analysis of dual-stage grid ion thruster

In order to study the extraction and acceleration mechanism of the dual-stage grid, a three-dimensional model based on the Particle-In-Cell/Monte Carlo Collision(PIC/MCC) method is performed. Dual-stage grid ion thruster is a new type of electrostatic ion thruster, which can break through the limitations of traditional gridded ion thrusters, and greatly improve the specific impulse. The high performance also makes the grid sensitive to operating parameters. In this paper,the influence of grid pa...     

基于核心问题导向的教学方法在实践课程中的应用

课程建设是学校学科建设的重要内容之一。针对《机场管制模拟训练》课程，围绕教学内容、教学方法、教学管理等方面分析现有教学环节中存在的不足，提出了基于核心问题导向的教学方法并开展课程建设。在教学模式上，提出“核心问题、知识范围、技能操作、情景意识”的四维知识重构方法，采用分享实践教学管理模式组织课程。教学实践表明，核心问题导向的教学方法有助于学生职业技能的提高和专业素养的培养。