吸附式压气机转子叶片气动优化设计

进行吸附式压气机转子叶片气动设计方法研究.提出通过迭代设计,应用三维流场计算结果提供S₂流面通流计算损失模型,提高了S₂流面流场计算精度;将最优化方法与数值模拟技术相结合,建立吸气与型面耦合的回转面二维叶型优化设计和三维叶片优化设计软件;应用所构建的设计软件,进行吸附式压气机转子设计,数值模拟结果表明:该转子在0.86的叶尖载荷下,设计点总压比为1.631、等熵效率为0.965,实现了高气动性能.      

U型进气管道对某离心压气机性能的影响

采用实验和数值模拟的方法研究了U型管道进气对某离心压气机性能的影响.实验结果显示,相比直管进气,U型管道进气在大流量工况下显著降低了压气机性能,压比、效率的下降量分别可达10%和18%以上.数值分析表明:U型管道进气时,其出口产生静压和总压畸变;压气机下游蜗壳因几何周向不均而存在相应的压力畸变,该畸变沿叶轮槽道向上游传播的过程中与进气畸变发生耦合.这种耦合作用改变了叶轮进口的流场结构,使叶轮槽道流量分布发生变化,叶轮对应畸变区域的熵值增加;同时还改变了叶片表面静压的分布形式,使整个叶轮主叶片的平均载荷增大约8%.      

浮升混合飞艇气动性能及总体参数分析

为了兼顾飞艇的气动性能和浮升特性,充分发挥二者的优势,并增强可控性,提出了一种基于NACA高升力翼型的组合嚢体式混合飞艇气动布局.采用计算流体力学(CFD)方法建立混合飞艇FLUENT计算模型,数值模拟了它在不同速度和迎角下的升阻特性、纵向静稳定性及浮升特性,并进行了总体性能评估,最后将其与常规飞艇进行了对比.结果表明:该组合嚢体飞艇布局具有较好的气动性能和效率,相同条件下提供的动升力为常规飞艇的3倍;当飞行速度大于26 m/s时,混合飞艇总升力效率开始大于常规飞艇,能够提供更好的浮升特性.此外,相同设计载荷下混合飞艇的外形尺寸更小,有利于增加有效载荷,可为低空大型混合飞艇的研发提供参考.      

量子点与TiO2电极参数对光阳极电子寿命及性能影响

通过对P25Ti O2光阳极薄膜厚度、敏化的量子点种类及量子点敏化方法研究,探讨了使用连续离子层吸附反应法的敏化方法(SILAR)时,P25Ti O2薄膜厚度与光阳极电子寿命的关系,以及量子点种类、共敏化工艺对光阳极光电性能的影响.采用电化学阻抗(EIS)、开路电压衰减(OCVD)及紫外-可见吸收方法,对影响光阳极光电性能的Ti O2薄膜厚度、量子点种类及共敏化工艺因素进行测试分析.实验结果表明:当光阳极薄膜厚度为12μm时,电子复合几率最小,光阳极的电子寿命相对最长;采用连续离子层吸附反应法(SILAR)对多种量子点共敏化的光阳极(Ti O2/Cd S/Cd Se/Zn S)与单一量子点敏化的光阳极(Ti O2/Cd S)相比,短路电流提高了34%,光转换效率提高了42%;合适的共敏化工艺也有助于提高光阳极的电子寿命、光谱吸收范围和吸收强度.     

可重复使用飞行器的保性能姿态跟踪控制方法

针对可重复使用飞行器再入姿态跟踪控制问题,在考虑执行器饱和、气动参数摄动和外部扰动的情况下,提出了一种保性能姿态跟踪控制方案。通过构造预设性能函数,使姿态跟踪误差在预先设置的包络内演化,保证了系统的瞬态和稳态性能;其次,借助于高增益扩张状态观测器解决了气动参数摄动和外部扰动的问题;之后,基于反步控制框架,设计了一种低复杂度的输出反馈扰动补偿控制方法,保证跟踪误差的收敛性。与已有方法相比,所设计的方法不包含一些复杂的非线性动力学近似技术,如神经网络等,降低了参数调节的复杂性,且无需对虚拟控制律重复微分,避免了"微分爆炸"问题。同时,Lyapunov稳定性分析表明,该方法能够保证误差变量的预期收敛以及其他闭环系统信号的有界性。最后,通过对比仿真验证了所提方法的有效性及可行性。     

背壁5-II材料高温热物理性能及微结构特征

研究了背壁5-II材料的密度、失重率和孔隙率随温度的变化规律,测试了温度对比定压热容、热导率的影响,研究了不同温度下和发动机长时间热试车下5-II材料的微结构特征。结果表明,5-II材料密度随温度升高而降低,热解后密度降至1.28 g/cm3,开孔率在30%左右;比定压热容随温度升高而增大,热导率随温度缓慢降低;随温度升高,其微结构特征表现为孔隙的大量增加和贯通,密度和孔隙率可作为固体发动机背壁热解失效的主要参量。     

Prescribed fast tracking control for flexible air-breathing hypersonic vehicles: An event-triggered case

In this paper, a prescribed fast tracking control scheme is proposed for Flexible Air-breathing Hypersonic Vehicles (FAHV) subject to lumped disturbances and limited resources. To maintain tracking errors of velocity and altitude converge to a predefined region with a prescribed time and release the transient intense fluctuations encountered in classical Prescribed Performance Control (PPC) using a fast decaying rate, a tracking differentiator-based PPC is presented, where the reaching time and the maximum time differentiation of preselected envelopes can be regulated as a prior via fixing an acceleration factor, so that a guaranteed fast convergence speed can be realized with reduced oscillations. Besides, to avoid the excessive occupation of limited resources (energy and communication) and guarantee a remarkable tracking accuracy, switching event-triggered mechanisms are constructed for FAHV control realization, which provide a promising way to pursue a desired level of tracking performance with a low energy consumption. Subsequently, Uncertainty and Disturbance Estimators (UDE) and Sigmoid function-based Tracking Differentiators (STD) are employed to provide disturbance estimation and reference derivation with a low computational complexity. Finally, robust control laws are designed to compensate for the sampling error induced by event-triggered conditions, meanwhile Zeno phenomena can be effectively eliminated. The simulation results and comparisons validate the effectiveness of the proposed scheme.     

火箭基组合循环发动机性能迭代算法研究

火箭基组合循环(简称RBCC)发动机性能分析模型的研究对于RBCC发动机结构的优化设计具有重要意义。本文结合RBCC发动机的结构特点和工作原理建立了RBCC发动机性能分析模型,并对RBCC发动机性能计算方法进行了研究。结合RBCC发动机引射模态和亚燃冲压模态的工作特点,通过迭代计算使进气道、混合段、燃烧室之间的参数耦合,实现了对RBCC发动机引射模态与亚燃冲压模态性能的快速分析。文章通过算例验证了算法的可行性,并通过与文献结果的对比验证了计算结果的可信度。     

基于预设性能的四旋翼无人机编队安全控制

针对四旋翼无人机编队系统存在模型不确定性、未知外部干扰与内部碰撞等问题,提出一种基于预设性能的安全控制方法。首先使用预设性能函数结合误差转换方法,将防止内部碰撞的不等式约束问题转换为无约束问题。同时针对模型中的不确定项,使用神经网络进行逼近;针对神经网络逼近误差与未知外部干扰组成的复合干扰,使用非线性干扰观测器进行估计,并分别设计位置与姿态子系统控制器,避免了编队内四旋翼无人机的碰撞。然后借助Lyapunov方法证明了闭环系统所有信号的收敛性。最后通过数值仿真验证了所提控制方法的有效性。     

Aerodynamic performance of owl-like airfoil undergoing bio-inspired flapping kinematics

Natural flyers have extraordinary flight skills and their prominent aerodynamic performance has attracted a lot of attention. However, the aerodynamic mechanism of birds' flapping wing kinematics still lacks in-depth understanding. In this paper, the aerodynamic performance of owl-like airfoil undergoing bio-inspired flapping kinematics extracted from a free-flying owl wing has been numerically investigated. The overset mesh technique is used to deal with the large range movements of flapping airfoils. The bio-inspired kinematics consist of plunging and pitching movement. A pure sinusoidal motion and a defined motion composed of plunging of sinusoidal motion and pitching of the bio-inspired kinematics are selected for comparison. The other two NACA airfoils are also selected to figure out the advantages of the owl-like airfoil. It is found that the cambered owl-like airfoil can enhance lift during the downstroke. The bio-inspired kinematics have an obvious advantage in lift generation with a presence of higher peak lift and positive lift over a wider proportion of the flapping cycle. Meanwhile, the bio-inspired motion is more economical for a lower power consumption compared with the sinusoidal motion. The sinusoidal flapping motion is better for thrust generation for a higher peak thrust value in both upstroke and downstroke, while the bio-inspired kinematics mainly generate thrust during the downstroke but produce more drag during the upstroke. The defined motion has similar lift performance with the bio-inspired kinematics, while it consumes more energy and generates less thrust. The unsteady flow field around airfoils is also analyzed to explain the corresponding phenomenon. The research in this paper is helpful to understand the flight mechanism of birds and to design a micro air vehicle with higher performance.