二级活塞式弹射机构动态仿真与分析

运用经典内弹道和气体动力学理论，建立了二级活塞式抛放弹弹射机构的数值计算模型，对某型号二级活塞式弹射机构工作的全过程进行了模拟计算，分析了不同参数对其弹射效果的影响，计算结果与实验结果相符，为该类型系统的进一步优化设计提供了理论依据。     

高空环境对航空遥感器光学窗口的影响

为提高航空遥感器光学窗口的光学性能,从空气动力学环境和大气环境两个方面分析了高空环境对光学窗口的影响。根据空气动力学原理,计算出飞行马赫数和雷诺数,以确定光学窗口所处的飞行环境;依据纵掠平壁理论,计算出光学窗口外表面的平均对流换热系数,仿真光学窗口温度分布,分析了轴向温差对光学窗口的影响。分析高空大气环境下光学窗口玻璃出现结霜原因及影响,并提出预防结霜的解决方案。最后针对某航空遥感器光学窗口进行飞行试验,结果表明分析的结论正确,提出的解决方案合理可靠,可为其他航空光学窗口设计提供依据。     

Unsteady RANS simulations of flow around a bridge section

This paper presents the results of unsteady Reynolds-averaged Navier-Stokes (URANS) simulations of flow around a common bridge deck geometry. Computations are performed with a noncommercial unstructured flow solver using two-dimensional hybrid meshes with fine near-wall resolution. The influence of different simulation parameters (grid refinement, time-step size, turbulence modelling) is analyzed, in particular in order to obtain flow solutions independent of spatial and temporal discretization. Results given by a one-equation eddy-viscosity turbulence model and a two-equation explicit algebraic Reynolds stress model are compared. Despite the limits imposed by the URANS approach and the relatively inexpensive two-dimensional computations, satisfactory agreement is found with the experimentally measured forces and pressures. These simulations help to explain the discrepancy between the results of two wind-tunnel test campaigns and show the dramatic influence of non-perfectly sharp edges on the global flow field development. The capability of the numerical approach to capture complex Reynolds number effects is also discussed.     

Field measurements of aerodynamic pressures in tunnels induced by high speed trains

The passage of high speed trains causes aerodynamic effects in tunnels, and considerable pressure transients are generated because of the restricted airspace within the tunnel. This leads to passenger discomfort, noise surrounding the tunnel, resistance to train movement, and possible damage to the train body and tunnel facilities. For the real assessment of the aerodynamic pressures in the tunnel induced by the passing trains of the high speed rail in Taiwan, a series of field measurements were performed near the portal and the shaft or the adit of the tunnel during normal operation. The measurements were conducted for several train speeds, including the maximum operation speed of the high speed rail in Taiwan, which is 300 km/h. Pressure sensors were deployed along the tunnel to investigate the propagation of pressure waves. The results show that the train nose entry/exit generated a compression wave propagating throughout the tunnel, resulting in a sharp increase in pressure. Conversely, the train tail entry/exit generated an expansion wave causing a pressure drop. The successive reflections of these pressure waves between both ends of the tunnel were observed. The pass-by of a train inside the tunnel also induced an immediate local pressure drop due to aerodynamic drag. Based on the measurement results, the spatial variation of the train-induced pressure peaks inside the tunnel is discussed. Furthermore, the relationship between the pressure peaks and the train speed is established, and the influence of the cross-sectional area of the tunnel is also presented.     

高速列车交会时的风致振动研究

摘 要：为了阐明高速列车交会过程中气动力对列车的系统动力学行为的影响,分别建立了CRH-2动车组的简化几何模型和50个自由度的车辆系统动力学模型。采用有限体积法对三维瞬态可压缩雷诺时均Navier-Stokes方程和k-e 两方程湍流模型进行求解,并通过滑移网格技术实现列车的运动,对考虑和不考虑气动力时的列车系统力学响应进行了数值模拟,并对两种情况下列车的安全性和舒适性进行了分析讨论。研究发现：气动力在列车交会过程中变化剧烈,对列车系统动力学行为的影响非常明显,交会时列车振动剧烈,头车和尾车的安全性和舒适性明显降低。     

垂直/短距起降飞机非线性动力学建模与仿真

垂直/短距起降(V/STOL)飞机具有广泛而高效的军事应用前景.为研究V/STOL飞机复杂的飞行控制问题,需要建立能够准确反映其动态特性且可用于飞行仿真的动力学模型.综合考虑V/STOL飞机的多进气道气流量变化、大迎角非线性和迟滞非定常特性、地面效应和喷气诱导效应等因素的影响,利用线性叠加原理并结合机理建模与经验公式,建立了全面的推进/气动力与力矩模型;在此基础上,基于刚体动力学和运动学原理,推导得到了V/STOL飞机的全状态六自由度非线性数学模型;最后,仿真分析了V/STOL飞机的地面效应和喷气诱导效应引起的动力学变化及其三角翼非定常动力学特性.结果表明:地面效应对V/STOL飞机动力学的影响可以忽略,而近地飞行时的喷气诱导效应会导致较大的升力损失,离地越近损失越大;V/STOL飞机的非定常动力学源于飞机迎角变化所引起的气动力滞环效应,且迎角越大、空速越小,滞环效应越显著,非定常动力学特性越强.所建模型物理意义明确、计算方便,能够较为准确地反映V/STOL飞机的动力学特性,可为其不同飞行模式下的模型简化应用和飞控系统设计提供帮助.     

600MW锅炉炉内气流流动特性的数值模拟

开展大型电站锅炉炉内气流流动特性的数值模拟,对于了解和掌握炉内气固多相流动特性、传热特性和燃烧过程具有十分重要的意义.本文在k-ε双方程湍流模型基础上,应用投影法,通过混合差分建立交错网格,对某600MW机组切向燃烧煤粉锅炉炉内气流的流动过程进行了计算机辅助数值试验(CAT).计算结果与冷态试验结果吻合较好.这对于预测炉内汽流结构具有很大的工程意义.     

皮卡车外流场的数值模拟

采用CFD进行皮卡车的外流场模拟,得到了车身表面压力分布、尾流典型剖面流速值和尾流流场结构,数值模拟结果与风洞试验结果吻合较好。模拟结果表明,皮卡车尾涡存在于货箱上方和尾挡板后方两个区域。进行了皮卡车几种几何改型的CFD模拟,所得阻力系数变化与实车试验结果有相同的变化趋势,证实了尾挡板的减阻作用。由此得出CFD用于皮卡车外流场模拟,可获得较高的模拟精度。     

扑翼飞行器的建模与控制研究进展

扑翼飞行器（Flapping-wing air vehicle,FAV）即通过模拟昆虫以及鸟类飞行方式而制造的仿生机器人.与常见的固定翼和旋翼飞行器相比,具有效率高、质量轻、机动性强、耗能低等显著优点,是飞行器发展的重要方向.关于扑翼机的研究始于上世纪后期,现如今从理论探索到机体开发都有了可喜的成果.本文首先介绍了世界领先的几款扑翼飞行器的特点,接着简述了扑翼飞行器在动力学、能源、控制等方面的发展现状,并对未来的研究方向做出了展望.