开口壁式涵道螺旋桨气动特性数值模拟

涵道共轴双螺旋桨以其结构紧凑、气动效率高、气动噪声低、安全可靠等性能和结构优点,已经被作为一种推力或升力装置广泛地应用到飞行器设计当中。涵道共轴双螺旋桨作为涵道共轴多旋翼飞行器的主升力系统,为了进一步提升其功率载荷和抗风性,文中采用数值模拟方法对其在悬停状态、轴流状态和斜流状态下的气动特性进行了计算分析。提出了开口壁式涵道螺旋桨的主升力系统构型,并对其气动性能进行了计算,得出了开口壁式涵道螺旋桨相比涵道共轴双螺旋桨所具有的优势。     

两种运动方式的直翼推进器水动力性能比较

针对直翼推进器在不同运动方式下水动力性能的变化,进行直翼推进器的非定常摆动运动方式(VSP)与定常回转运动方式(KBP)的理论研究,分别实现了推进器叶片随公转运动的同时进行匀速自转或变速自转的多叶片耦合运动.结合VSP实际应用的翼型与KBP特殊运动特性决定的翼型进行对比分析,在充分发挥VSP水动力性能的基础上,运用CF...     

Tomography-like flow visualization of a hypersonic inward-turning inlet

The flow field in a typical inward-turning inlet was visualized using the Planar Laser Scattering (PLS) method in a shock tunnel with a nominal Mach number of 6. The opaque inlet, which is truncated at a series of sections, and the following transparent isolator, are combined to enable the optical access at different streamwise locations. The sequential PLS images provide a tomography-like flow visualization, which confirm the existence of streamwise Counter-rotating Vortex Pairs (CVPs) in both external and internal flow field of the inlet. Generation mechanisms of these CVPs are unraveled with the help of a numerical simulation, among which the cowl notch plays an important role in the generation of surface trailing CVPs along the centerline of the cowl. Moreover, the cowl shock sweeps the internal boundary layer towards the body side, which ultimately accumulates low-momentum flow on the body side in forms of a large CVP propagating downstream through the isolator. The CVPs formed in the shape-transition are responsible for the nonuniform flow field of the inward-turning inlet. This study indicates that the V-shaped cowl notch affects the downstream flow significantly and, therefore, should be examined thoroughly in practical applications.     

螺旋桨滑流对短舱/机翼构型尾迹流场的影响

螺旋桨滑流对飞机机翼表面流动和尾迹流场有重要的影响,进而改变机翼和飞机的性能。本文通过风洞试验方法开展了螺旋桨滑流对尾迹流场的影响研究。试验模型为后掠角4°、带增升装置的螺旋桨/短舱/机翼模型,试验构型包括襟翼收回和襟翼打开,试验策略是在两种构型下分别同时模拟真实飞行状态的拉力系数和前进比。通过比较有/无螺旋桨时空间尾迹流场的速度场和流动偏角等,分析滑流在尾迹流场中的发展规律和影响范围,研究尾迹流场中滑流的加速效应、下洗和侧洗效应等。结果表明,在滑流作用下,机翼远后方流场参数在机翼展向和垂直方向上均呈现复杂的变化;同时,襟翼收回和襟翼打开构型的滑流效应有明显的区别,影响规律也有所不同。     

Analysis and control of inter-electrode gap during leveling process in counter-rotating electrochemical machining

The inter-electrode gap (IEG) is an essential parameter for the anode shaping process in electrochemical machining (ECM) and directly affects the machining accuracy. In this paper, the IEG during the leveling process of an oval anode workpiece in counter-rotating ECM (CRECM) is investigated. The variation of the minimum IEG is analyzed theoretically, and the results indicate that rather than reaching equilibrium, the minimum IEG in CRECM expands constantly when a constant feed speed is used for the cathode tool. This IEG expansion leads to a poor localization effect and has an adverse influence on the roundness of the machined workpiece. To maintain a small constant IEG in CRECM, a variable feed speed is used for the cathode based on a fitted equation. The theoretical results show that the minimum IEG can be controlled at a small value by using an accelerated feed speed. Experiments have been conducted using a specific experimental apparatus in which the cathode tool is designed as a combined structure of two sectors and a thin sheet. By detecting the machining currents flowing through the minimum IEG, how the latter varies is obtained indirectly. The results indicate that using an accelerated feed speed is effective for controlling the IEG, thereby improving the roundness of the machined workpiece.     

高速直升机涵道风扇矢量推进系统模型悬停状态的气动力测量研究

为了提高直升机的飞行速度,出现了用涵道风扇矢量推力系统取代常规的尾桨和尾翼的复合式高速直升机.然而,涵道风扇矢量推进系统各部件间相互作用很复杂,从理论上确定涵道风扇矢量推进系统的气动特性尚有相当难度,为了研究涵道风扇矢量推进系统气动特性,利用涵道风扇矢量推进系统试验模型,通过试验实测该系统在轴流状态的气动力及舵面偏角和设计参数对系统气动力的影响,得到了一些涵道风扇矢量推进系统所特有的气动现象,其结果可作为理论建模的依据.     

活塞发动机与无人机性能匹配分析

活塞发动机由于其自身的性能和价格优势广泛用作无人机的动力,本文介绍了在无人机概念设计阶段如何进行活塞发动机的选择及相应的螺旋桨的选配,用到的都是经验公式及经验曲线,简单实用。文章还统计了一些使用螺旋桨发动机的无人机及一些活塞发动机的主要技术参数。     

一种涵道螺旋桨优化设计新方法研究

根据Theodorsen的片条理论、涵道后缘的库塔条件以及边界页微元涡丝的诱导方程,构筑了涵道螺旋桨叶片涡强度分布的计算模型,用该模型代替Prandtl的动量损失函数及环量函数,将自由螺旋桨的最小能量损失的设计方法加以推广,优化设计了涵道螺旋桨。     

螺旋桨流场Euler/NS数值解对比分析

采用多块点对点网格生成技术,生成螺旋桨流场空间计算网格。针对不同前进比,分别求解Euler和NS方程对螺旋桨流场进行数值模拟,并与实验结果进行了对比分析。研究发现无粘和有粘的计算结果均接近于实验结果,因此基于Euler方程的流场数值模拟更适用于工程设计。     

平流层飞艇螺旋桨地面风洞试验

按照等雷诺数Re和等前进比λ相似准则,从平流层飞艇螺旋桨的运动和动力相似角度出发,建立了螺旋桨拉力系数、功率系数和效率等参数的相似公式,并在地面常规密度风洞中进行了螺旋桨的缩比模型试验.通过对有关试验结果与平流层原型桨的数值模拟和片条理论计算结果的对比分析可看出,三者基本吻合,从而说明地面风洞试验的环境密度大小基本不影响螺旋桨相似性参数,由此得到平流层飞艇螺旋桨可在地面常规密度风洞中按照等Re和等前进比相似准则进行缩比模型试验,而不必为此建立特制的昂贵的低密度环境风洞.同时,实验结果表明,在螺旋桨前进比小于0.3时的情况下,因滑流区侧向收缩大,片条理论计算的无量纲气动性能曲线需要进行侧收缩修正.