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991.
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993.
分析了民航客机燃油效率的影响因素,将气动阻力进行分解,推导出了以巡航效率为优化目标的最佳机翼优化方法。算例表明,无论是在飞机的方案设计阶段,还是在详细设计阶段,方法都是适用的。方法不仅可用于最佳机翼面积的优化工作,在详细设计阶段,还可用于检验飞机的气动优化设计是否偏离飞机的优化目标,以及检验飞机的最佳巡航航程指标是否与最佳燃油效率匹配。 相似文献
994.
995.
《中国航空学报》2016,(5):1196-1204
The flow fields over a generic cranked double delta wing were investigated. Pressure and velocity distributions were obtained using a Pitot tube and a hot wire anemometer. Two different leading edge shapes, namely ‘‘sharp" and ‘‘round", were applied to the wing. The wing had two sweep angles of 55° and 30°. The experiments were conducted in a closed circuit wind tunnel at velocity 20 m/s and angles of attack of 5°–20° with the step of 5°. The Reynolds number of the model was about 2 ×10~5 according to the root chord. A dual vortex structure was formed above the wing surface. A pressure drop occurred at the vortex core and the root mean square of the measured velocity increased at the core of the vortices, reflecting the instability of the flow in that region. The magnitude of power spectral density increased strongly in spanwise direction and had the maximum value at the vortex core. By increasing the angle of attack, the pressure drop increased and the vortices became wider; the vortices moved inboard along the wing, and away from the surface; the flow separation was initiated from the outer portion of the wing and developed to its inner part. The vortices of the wing of the sharp leading edge were stronger than those of the round one. 相似文献
996.
《中国航空学报》2016,(6):1553-1562
This paper deals with the numerical solution of inviscid compressible flows. The threedimensional Euler equations describing the mentioned problem are presented and solved numerically with the finite volume method. The evaluation of the numerical flux at the interfaces is performed by using the Toro Vazquez-Harten Lax Leer(TV-HLL) scheme. An essential feature of the proposed scheme is to associate two systems of differential equations, called the advection system and the pressure system. It can be implemented with a very simple manner in the standard finite volume Euler and Navier–Stokes codes as extremely simple task. The scheme is applied to some test problems covering a wide spectrum of Mach numbers, including hypersonic, low speed flow and three-dimensional aerodynamics applications. 相似文献
997.
钝头体窄条翼布局导弹在大攻角下拥有极为优异的纵向气动特性,但横向容易失稳,做快速机动时容易诱发非指令的横向不稳定运动。通过开展高速风洞自由摇滚试验和数值模拟,研究了窄条翼导弹自由摇滚特性和流动机理,试验与计算吻合较好。研究发现:较大迎角时,窄条翼面积中心距离尾舵前缘根部5~6倍直径时,模型会进入极限环摇滚,窄条翼位置对模型稳定性有显著的影响,去掉窄条翼或尾舵时,模型均不会进入摇滚;模型空间流场特性表明,气流经过窄条翼时形成的片涡,对背风舵产生强烈的干扰,抑制了尾舵涡的形成和发展,使背风舵动态失稳,导致模型进入极限环摇滚。 相似文献
998.
999.
An autonomous approach and landing (A&L) guidance law is presented in this paper for landing an unpowered reusable launch vehicle (RLV) at the designated runway touchdown.Considering the full nonlinear point-mass dynamics,a guidance scheme is developed in threedimensional space.In order to guarantee a successful A&L movement,the multiple sliding surfaces guidance (MSSG) technique is applied to derive the closed-loop guidance law,which stems from higher order sliding mode control theory and has advantage in the finite time reaching property.The global stability of the proposed guidance approach is proved by the Lyapunov-based method.The designed guidance law can generate new trajectories on-line without any specific requirement on off-line analysis except for the information on the boundary conditions of the A&L phase and instantaneous states of the RLV.Therefore,the designed guidance law is flexible enough to target different touchdown points on the runway and is capable of dealing with large initial condition errors resulted from the previous flight phase.Finally,simulation results show the effectiveness of the proposed guidance law in different scenarios. 相似文献
1000.
根据ASTM标准设计了复合材料沉头螺栓单钉单搭接头拉伸性能试样,并完成试验件的制备和挤压性能试验。试验过程中采用非接触全场应变测量系统(VIC-3D)对载荷-位移曲线、表面应变场、沉头板上表面面外位移等试验数据进行了采集。基于Abaqus/Standard和Abaqus/Explicit模块建立了复材接头单向拉伸的静力隐式和动力显式三维有限元模型,利用模型搭接区域的变形对试验结果进行验证。采用静力隐式算法所得接头挤压刚度和层合板上表面末端面外位移与试验值的误差分别为14.4%和20.5%;采用动力显式算法所得接头挤压刚度和层合板上表面末端面外位移与试验值的误差分别为13.1%和11.9%。采用动力显式算法精度较高,而且其在接触建模时稳健性很强,可用于后续多钉连接接头以及整体壁板等大型复杂结构建模。 相似文献