无人机伞回收动力学分析

在建立无人机六自由度飞行力学模型和降落伞回收动力学模型的基础上,对无人机的整个回收过程进行仿真分析,并与飞行试验进行了比较。结果表明:本文所采用的方法较为准确地预测了整个减速伞工作阶段中的相关动力学特性。计算结果还包括了无人机与回收系统的相对运动过程,有效地预测了回收过程的危险情况,为无人机控制律和回收系统设计提供了重要参考。     

边条翼下进气道与飞机一体化流场特性的研究

利用雷诺平均可压缩N-S方程以及可实现k-ε模型,对边条翼下进气的飞机进行了内外流场的气动耦合计算,研究分析了边条翼下进气道进口处的局部流场特性,说明了局部流场特性随攻角变化的关系,数值模拟与实验结果吻合较好.通过改变进气道的流量系数,分析飞机流场的变化,重点阐明了进气道流量系数对边条涡破碎位置的影响以及机理,即:进气道流量系数越低,涡的破碎位置就越提前,会影响飞机的气动性能.这为今后进一步研究奠定了坚实的基础.     

太阳帆航天器被动姿态控制研究

针对由有效载荷、太阳帆和4个控制叶片所组成的太阳帆航天器系统,从物理模型出发,利用欧拉方程建立了姿态动力学模型,并通过数值仿真对太阳帆航天器基于控制叶片的对日定向性能进行了研究。研究结果表明,在行星际飞行中太阳帆航天器可以通过使控制叶片保持偏置来保持姿态稳定。     

航天器虚拟动态试验技术研究及展望

文章简要回顾了航天器结构动态设计技术的发展,并且指出随着现代航天器越来越复杂,数值分析方法与动态试验方法都无法满足设计的要求。为了解决这个问题,必须采用虚拟动态试验技术。文中较详细地介绍了复杂结构模型修改新技术、虚拟模态试验技术和振动台虚拟振动试验技术。文章最后还对该领域未来研究方向进行了展望。     

LES of film cooling for different jet fluids

The present paper investigates the impact of the velocity and density ratio on the turbulent mixing process in gas turbine blade film cooling.A cooling fluid is injected from an inclined pipe at α=30° into a turbulent boundary layer profile at a freestream Reynolds number of Re∞=400000.This jet-in-a-crossflow(JICF) problem is investigated using large-eddy simulations(LES).The governing equations comprise the Navier-Stokes equations plus additional transport equations for several species to simulate a non-reacting gas mixture.A variation of the density ratio is simulated by the heat-mass transfer analogy,i.e.,gases of different density are effused into an an air crossflow at a constant temperature.An efficient large-eddy simulation method for low subsonic flows based on an implicit dual time-stepping scheme combined with low Mach number preconditioning is applied.The numerical results and experimental velocity data measured using two-component particle-image velocimetry (PIV) are in excellent agreement.The results show the dynamics of the flow field in the vicinity of the jet hole,i.e.,the recirculation region and the inclination of the shear layers,to be mainly determined by the velocity ratio.However,evaluating the cooling efficiency downstream of the jet hole the mass flux ratio proves to be the dominant similarity parameter,i.e.,the density ratio between the fluids and the velocity ratio have to be considered.      

复杂积冰翼型气动性能分析

为了克服复杂外形难以划分结构化网格的问题, 采用结构/非结构混合多块网格对复杂积冰翼型的气动性能-进行了分析计算.在靠近积冰边界的内层采用了非结构网格, 在非结构网格外采用结构化网格以节省存储空间和计算时间.不同类型网格之间采用了点点对接的方式以简化通量重构的处理方式.整个流动区域采用SST湍流模型, 求解了雷诺平均N-S方程.数值计算结果表明结构/非结构混合多块网格在复杂积冰翼型气动性能计算上的可行性, 积冰对翼型的气动性能造成了严重的影响.      

Numerical study of a 3.5-stage axial compressor at on-and off-design conditions

Numerical investigation is conducted on a 3.5-stage axial compressor,on which numerous experimental projects were carried out at the Institute during the last years and an experimental database was established.In the current study five on-and off-design operating points are simulated using a RANS solver and the results are compared with the measurement.The result shows that the compressor performance can be qualitatively predicted by the mixing-plane method.Better agreement is obtained for the on-design operating point.However,as the flow unsteadiness is insufficiently considered,the numerical method produces end-wall low-speed flow layers accumulated with the flow passing through the passage,which is in no good agreement with the experimental data.In the numerical simulation the rotor rows receive less work and this difference from the measurement increases with the rotational speed.In contrast,the stator rows increase the pressure more efficiently than the measurement.In the simulation the flow in the last stator row tends more to separate on the pressure side of the blade.For the operating points close to the surge line,the predicted separation is more intense than the experimental observation.But for the operating points close to the choke,the separation is suppressed.      

轴流压气机过失速的非线性动力学分析

为了解Greitzer的B参数和节流γ参数对轴流压气机过失速行为的影响, 使用分叉分析方法, 研究了压缩系统中过失速所对应的静态分叉行为.由此, 划分了γ-β分叉参数空间中, 轴流压缩系统稳定和不稳定流动的区域分布图.结果表明, 非线性动力学的分叉分析方法, 可以准确的捕捉到轴流压缩系统中典型的过失速流动行为, 同时可以简便的分析分叉参数作用下平衡点稳定性的变化情况.      

空间机器人柔性臂动力学模糊控制的研究

重点研究了在空间机器人柔性臂的动力学非线性控制问题,由于柔性臂动力学系统的强非线性和耦合性,使得柔性臂控制系统复杂,控制的实时性和稳定性差,本文针对以往柔性臂控制所存在的问题,综合考虑系统的动态和静态特性,提出了一种带有非线性补偿器及ＰＩＤ控制器的柔性臂模糊复合控制方案,然后,根据所推导了一两连杆的空间机器人柔性臂的这非线性模型,进行了系统控制的仿真研究,实例仿真的结果表明,该控制方案能有效地抑制     

电液主动控制挤压油膜阻尼器的理论分析

针对旋转机械采用传统的动压轴承构成的挤压油膜阻尼器存在的问题,提出了一种由压电晶体-电液主动控制的动静压混合轴承构成的电液挤压油膜阻尼器(HSFD).对于这种电液挤压油膜阻尼器, 经典的半油膜(π油膜)假设不再成立. 为了求解它的压力分布, 提出了一种适用于含有动静压混合作用时Reynolds方程的求解方法. 在此基础上, 对采用这种电液挤压油膜阻尼器的转子系统进行了理论分析, 从而为实现主动控制奠定了基础.