共查询到19条相似文献,搜索用时 171 毫秒
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蜻蜓翅膀具有独特的褶皱状形貌.研究者们致力于利用仿生学原理,设计在低雷诺数条件下具有更优气动性能的褶皱翼型.本文采用计算流体力学方法,求解二维不可压Navier-Stokes方程组,探讨了四种翼型(平板翼型、流线翼型、小幅度褶皱翼型和大幅度褶皱翼型)的气动表现.在低雷诺数条件下得到以下结果:(1) 较小幅度的褶皱结构有利于增加升力和减小阻力.(2) 雷诺数变化时褶皱翼型的升力系数呈非线性变化;在特定雷诺数区间,幅度相近的褶皱翼型会发生相对气动优势的转变.(3) 褶皱结构内的回流区通过减小粘性阻力,使得翼型总阻力下降.(4) 翼型前缘的极小区域会产生脉冲高升力,对升力表现产生较大影响.这些结果表明,调整褶皱幅度是实现褶皱翼型气动优化的有效方案. 相似文献
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支撑干扰修正一直是风洞试验的一个重点和难点,特别是对于尾部扁平的飞翼布局飞行器,阻力和俯仰力矩是一个小量,进行风洞试验时,尾部需要局部放大,对阻力和俯仰力矩的影响相对较大,这就使得风洞试验时对支撑影响修正方法提出了更高的要求。本文采用CFD数值模拟手段针对小展弦比飞翼标模开展了网格收敛性和支撑干扰影响研究,分析了尾支撑对飞翼气动特性、压力分布和流场结构的影响,为进一步开展风洞试验的支撑干扰修正提供了依据。在典型工况下,支撑干扰会导致升力系数减小,阻力系数减小,抬头力矩增大;试验模型后体放大和支撑存在会导致飞翼标模上表面压力增大,激波强度变弱,尾部分离区域减小。 相似文献
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高速电梯机械系统KED分析与动态性能优化 总被引:1,自引:0,他引:1
建立了高速电梯机械系统的运动微分方程,对运动微分方程提出了基于KED分析的求解方法。为了改善高速电梯动态性能,在电梯机械系统KED分析的基础上,提出了一种以降低轿厢最大振动加速度幅值为目标的动态性能优化方法。用本文方法对TKJT100/1.6-JXPC型电梯进行了KED分析与动态性能优化,得到了令人满意的结果。 相似文献
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旋风分离器减阻杆结构及减阻前后流场的测定与分析 总被引:11,自引:0,他引:11
报告了在旋风分离器内安装不同断面形状及尺寸的细杆(简称减阻杆)后对流动阻力降低及安装减阻杆前后旋风分离器内流场变化的测定结果,得出了减阻幅度与减阻杆插入长度和迎风面积及背风面曲率半径成正比、减阻杆使切向速度及轴向速度梯度减小、径向上静压梯度减小和轴向上逆压梯度减小等结论.本文同时对减阻杆的减阻机理及减阻时保证分离效率或提高分离效率的原因进行了分析. 相似文献
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高速列车头型长细比对气动噪声的影响 总被引:1,自引:0,他引:1
高速列车的头尾车外形对气动噪声具有重要的影响.工程实践中随着车速的增加,车辆头部越来越细长,日本高速磁悬浮列车实践中甚至出现了具有极端长细比的头部形状.本文以讨论头型长细比对列车气动噪声的影响规律为出发点,应用非线性声学求解器(NLAS)和FW-H声学比拟法的混合算法,在3种运行速度下对基于CRH380A高速列车头型概化的4种不同头型长细比的模型车的气动噪声进行了数值模拟.给出了不同头型长细比列车的流场特征、气动阻力和气动噪声.结果表明,列车的气动总阻力随头型长细比的增大而减小,且头型长细比对列车总气动阻力的影响随运行速度的增加而增强.而头型长细比对气动噪声的影响呈现出较为复杂的影响,并不存在单调的影响关系;综合考虑气动阻力和气动噪声,长细比最大的头型综合性能较优,但差异并不显著,因此在不考虑微气压波等因素的条件下,简单增加车头长细比并不一定能带来明显的气动噪声性能提升. 相似文献
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《应用力学学报》2018,(6)
设计了一种斜出口零质量射流激励器并将其应用于垂直轴风力机。对施加零质量射流激励器的直线翼垂直轴风力机进行了数值研究。为适应垂直轴风力机运行工况,提出了一种冲程长度随方位角变化的激励器控制策略,验证其减小激励能耗及改善流场结构的特点;分析了射流孔数量及冲程长度对控制叶片流动分离及提升风力机气动性能的影响规律,并在最佳控制参数下对风力机流场结构进行了分析。结果表明:当激励器布置于叶片后部,最大射流吹气系数为0.0506时,采用该种激励器控制策略下的双射流孔风力机,风能利用系数相比未施加流动控制、定常吹气、定冲程长度最大分别提升21.31%、3.98%、0.06%,且射流孔数越多,提升效果越差。该种流动控制技术可抑制大涡的形成及发展,改善叶片周围流场结构。 相似文献
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采用较为合理的计算流体力学分析技术对汽车高速行驶时其外部气动特
性进行研究. 以带有轮胎、侧后视镜以及天线等突出部件的某轿车外流场模型为研究对象,
在稳态下采用RNS法中Realizable $k$-$\varepsilon$两方程湍流模型结合增强壁
面函数法对不同车速工况下整车外流场进行数值仿真计算. 研究表明:沿车辆X纵
向上所形成压力差是产生气动阻力的主要原因; 随车速的提高, 气动阻力
的增长速度快于气动升力的增长. 相似文献
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临近空间飞行器存在多种不同的布局形式,而针对不同气动布局概念之间的系统研究则相对缺乏.采用数值模拟方法,对临近空间飞行器三类典型气动布局概念--扁平升力体、翼身融合体和翼身组合体开展系统的计算与分析,通过对比不同布局的升阻特性、静稳定特性、舵效特性等,获得不同布局概念气动性能优劣的初步评估.结果表明:扁平升力体的升力和阻力比较大,升阻比最低,容积率则最大,侧向稳定性最好;翼身组合体的升力和阻力比较小,升阻比最高,容积率比较低,侧向静稳定性较差;翼身融合体布局的特性介于翼身组合体和扁平升力体布局之间. 相似文献
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Yi Yang Huida Zhang Zhaodi Hong 《International Journal of Computational Fluid Dynamics》2019,33(1-2):77-86
The vacuum pipeline vehicle system is a novel conceptual system aimed to provide a high-speed public transportation service in the future, featured with a reduced-pressure tube in which pressurised capsules ride on a cushion of air that is driven by a combination of linear induction motors and air compressor. The capsule body has a great influence on the aerodynamic performance of vehicles. This work involves numerical simulations based on finite volume method to study the optimisation method for the parameter design of the vehicle body. The results show that the aerodynamic resistance of the optimised vehicle is further reduced, the drag reduction rate reaches 5.52%, and the speed of the Kantrowitz limit phenomenon is delayed from 760 to 860?km/h. The drag reduction effect is obvious. 相似文献
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A new bionic MAV's flapping motion based on fruit fly hovering at low Reynolds number 总被引:1,自引:0,他引:1
On the basis of the studies on the high unsteady aerodynamic mechanisms of the fruit fly hovering the aerodynamic advantages
and disadvantages of the fruit fly flapping motion were analyzed. A new bionic flapping motion was proposed to weaken the
disadvantages and maintain the advantages, it may be used in the designing and manufacturing of the micro air vehicles (MAV’s).
The translation of the new bionic flapping motion is the same as that of fruit fly flapping motion. However, the rotation
of the new bionic flapping motion is different. It is not a pitching-up rotation as the fruit fly flapping motion, but a pitching-down
rotation at the beginning and the end of a stroke. The numerical method of 3rd-order Roe scheme developed by Rogers was used
to study these questions. The correctness of the numerical method and the computational program was justified by comparing
the present CFD results of the fruit fly flapping motion in three modes, i.e., the advanced mode, the symmetrical mode and
the delayed mode, with Dickinson’s experimental results. They agreed with each other very well. Subsequently, the aerodynamic
characteristics of the new bionic flapping motion in three modes were also numerically simulated, and were compared with those
of the fruit fly flapping. The conclusions could be drawn that the high unsteady lift mechanism of the fruit fly hovering
is also effectively utilized by this new bionic flapping. Compared with the fruit fly flapping, the unsteady drag of the new
flapping decreases very much and the ratio of lift to drag increases greatly. And the great discrepancies among the mean lifts
of three flapping modes of the fruit fly hovering are effectively smoothed in the new flapping. On the other hand, this new
bionic flapping motion should be realized more easily. Finally, it must be pointed out that the above conclusions were just
drawn for the hovering flapping motion. And the aerodynamic characteristics of the new bionic flapping motion in forward flight
are going to be studied in the next step.
The project supported by the National Natural Science Foundation of China (10232010, 10032060, 90605005). 相似文献
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Experimental investigation on the flow around a simplified geometry of automotive engine compartment
In the current sustainable development context, car manufacturers have to keep doing efforts to reduce the aerodynamic drag
of automotive vehicle in order to decrease their CO2 and greenhouse gas emissions. The cooling airflow, through the engine compartment of vehicles, contributes from 5 to 10%
to the total aerodynamic drag. By means of simplified car geometry, equipped with an engine compartment, the configurations
that favor a low contribution to total drag are identified. PIV (particle image velocimetry) velocity measurements in the
wake of the geometry allow explaining these drag reductions. Besides, the cooling flow rate is also assessed and gives indications
on the configurations that favor the engine cooling. 相似文献
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基于局部型函数三维参数化方法、改进的蚁群算法和改进的克里金(Kriging)代理模型,开展了列车头型的三维气动减阻优化设计研究。为了避免复杂几何外形大变形情况下千万量级网格的重复生成,提高高速列车头型优化设计的效率,引入了缩减控制点的径向基函数网格变形技术。优化结果表明:径向基函数网格变形技术在不降低网格质量的情况下可以有效缩短网格变形的时间消耗,能够用于复杂几何外形的气动优化设计;在给定的设计空间内,控制鼻锥外形的6个关键设计参数对列车气动阻力的影响呈单调递增关系;优化后,在满足约束条件的情况下,简化外形列车的整车气动阻力减小5.41%,头尾车减阻效果明显,中间车气动阻力基本不变。 相似文献
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The Magnus effect is well known phenomena for producing high lift values from spinning symmetrical geometries such as cylinders, spheres, or disks. But, the Magnus force may also be produced by treadmill motion of aerodynamic bodies. To accomplish this, the skin of aerodynamic bodies may circulate with a constant circumferential speed. Here, a novel wing with treadmill motion of skin is introduced which may generate lift at zero air speeds. The new wing may lead to micro aerial vehicle configurations for vertical take-off or landing. To prove the concept, the NACA0015 aerofoil section with circulating skin is computationally investigated. Two cases of stationary air and moving air are studied. It is observed that lift can be generated in stationary air although drag force is also high. For moving air, the lift and drag forces may be adopted between the incidence angles 20° to 25° where lift can posses high values and drag can remain moderate. 相似文献
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JAN-KAUNG FU SHEN-MIN LIANG 《International Journal of Computational Fluid Dynamics》2013,27(3):249-273
ABSTRACT A numerical study is made to analyze the performance of a secant-ogive-cylinder projectile in the transonic regime in terms of aerodynamic drag. At transonic speeds, the base drag contributes a major portion of the total aerodynamic drag, and hence affects projectile's performances significantly. The base bleed method is applied to reduce the base drag by varying the value of parameters, the bleed quantity (I) and the bleed area ratio (?). The implicit, diagonalized, symmetric Total Variation Diminishing (TVD) scheme, accompanied by a suitable grid, is employed to solve the thin-layer axisymmetric Navier-Stokes equations coupled with the Baldwin-Lomax turbulence model. The computed results show that, in comparison with the case without base bleed, an increase in bleed quantity or a higher injection speed due to a smaller bleed area ratio at fixed bleed quantity can result in a base (and total) drag reduction. At Mach number 0.96, the reductions in base drag and total drag can be as high as 64% and 44%, respectively, for I = 0.1 and ? = 0.3. 相似文献
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Reynolds-averaged Navier-Stokes simulations based on second-order numerical methods are widely used by commercial codes and work as dominating tools for most industrial applications. They, however, suffer from limitations in accurate and reliable predictions of skin-friction drag and aerodynamic heating, as well as in simulations of complex flows such as large-scale separation and transition. A remedy for this is the development of high-order schemes, by which numerically induced dissipation and dispersion errors of low-order schemes can be effectively reduced. Weighted compact nonlinear schemes (WCNSs) are a family of high-resolution nonlinear shock-capturing methods. A stencil-selection procedure is introduced in the proposed work with an aim to improve the nonlinear weight of the third-order WCNS. By using the approximate dispersion relation analysis, it is demonstrated that the new scheme has reduced dissipation and dispersion errors, compared with WCNSs using two typical nonlinear weights. Improvements are also achieved by the new scheme in numerical tests such as the double Mach reflection problem and the Rayleigh-Taylor instability simulation, which are characterized by strong shock discontinuities and rich small scales, respectively. The new scheme is therefore highly favored in the simulation of flow problems involving strong discontinuities and multiscales phenomena. 相似文献