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1.
基于雷诺平均Navier-Stokes粘性流动方程,采用数值模拟方法,分析了吹气控制对多段翼型气动性能的影响,阐述了吹气改善多段翼型流动的机理。采用有限体积法对雷诺平均Navier-Stokes方程进行空间离散,时间方向推进采用二阶迎风格式,湍流模型采用SST k-ω模型。结果表明:在多段翼型基础上采取吹气控制可以获得很好的气动增升效果,三段翼型的最大升力系数可达4.98;吹气可改善多段翼型表面流动,减小其流动分离,增加升力;在同样的吹气口几何参数条件下,在一定范围内增大吹气动量系数可以提高多段翼型的升力系数;在多段翼型主翼后段和襟翼同时施加吹气流动控制可以获得更好的效果,升力系数比基本三段翼型(基本构型A)增加30.05%。 相似文献
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论文通过数值模拟方法对NACA6412层流翼型的低速绕流特性进行了研究,采用修正的BaldwinLomax湍流模型对来流速度为25m/s、8°迎角时翼型的流场、背风区的速度型分布、不同弦向位置附面层厚度的变化规律以及转捩位置进行了模拟,数值模拟结果与风洞实验结果具有一定的相关性. 相似文献
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大型低速二元风洞侧壁边界层控制及对单段翼型实验结果的影响 总被引:1,自引:0,他引:1
本文简述了NF-3风洞二元实验段侧壁边界层吹除控制系统及具有吹气的模型实验方法,给出了不同吹气系数对风洞边界层的控制效果以及对相对厚度为7%的单段翼型实验结果的影响。初步实验研究结果表明,该控制系统能有效地改善风洞侧壁边界层的流动状态,减小侧壁干扰,改善翼型实验中的二元流动特性 相似文献
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在二元翼型风洞实验段中的侧壁边界层将引起模型展向流动的不均匀性,使预想的二元流动受到三元扭曲,引起实验数据的误差,目前消除或减少侧壁干扰的有效方法之一是采用侧壁抽吸技术。本文就抽吸的有效性,抽吸区域和阻尼材料等问题进行了讨论和分析,并对抽吸技术中的问题提出了一些看法。 相似文献
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对称翼型低雷诺数小攻角升力系数非线性现象研究 总被引:12,自引:0,他引:12
采用Rogers发展的三阶Roe格式,求解非定常不可压N-S方程,时间方向为二阶精度双时间步方法, 数值模拟了对称翼型SD8020低雷诺数(Re=40000,100000)条件下,流场层流分离涡结构和升力系数随攻角的变化.同试验比较证明了数值模拟的正确性.通过对数值模拟时均化流场结果的详细分析,发现对称翼型在小雷诺数0°攻角附近出现的层流分离泡,其内部结构和演化规律都不同于经典层流分离泡模型,从而提出了一种后缘层流分离泡模型.并应用该模型对对称翼型小攻角低雷诺数流场特性以及升力系数非线性效应的形成机理进行了研究和解释. 相似文献
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基于$k$-$\omega$的SST两方程湍流模型, 求解雷诺平均N-S方程获得定常和非定常气动力, 耦合
翼型弹性振动方程, 在时间域内模拟了不同的翼型非定常流动, 重点研究了大迎角下的分离
流问题, 研究结果表明: 在百万雷诺数条件下, 由于振动引起分离涡的不规律脱落, 可能导
致气动力平均值的变化; 而厚度大于20\%的翼型在一定大迎角范围内, 会出现分离涡流场平
衡态的转化, 从流体力学稳定性的角度, 解释了风洞实验中大迎角气动力数据的分散性, 为
大迎角气动力风洞实验的重复性和数据分散性给出了一种新解释. 相似文献
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低雷诺数翼型蒙皮主动振动气动特性及流场结构数值研究 总被引:1,自引:0,他引:1
针对低雷诺数(Re)翼型气动性能差的特点,文章通过对翼型柔性蒙皮施加主动振动的方法,提高翼型低Re下的气动特性,改善其流场结构.采用带预处理技术的Roe方法求解非定常可压缩Navier-Stokes方程,对NACA4415翼型低Re流动展开数值模拟.通过时均化和非定常方法对比柔性蒙皮固定和振动两种状态下的升阻力气动特性和层流分离流动结构.初步研究工作表明在低Re下柔性蒙皮采用合适的振幅和频率,时均化升阻力特性显著提高,分离泡结构由后缘层流分离泡转变为近似的经典长层流分离泡,分离点后移,分离区缩小.在此基础上,文章更加细致研究了柔性蒙皮两种状态下单周期内的层流分离结构及壁面压力系数分布非定常特性和演化规律.蒙皮固定状态下分离区前部流场结构和压力分布基本保持稳定,表现为近似定常分离,仅在后缘位置出现类似于卡门涡街的非定常流动现象.柔性蒙皮振动时从分离点附近开始便产生分离涡,并不断向下游移动、脱落,表现为非定常分离并出现大范围的压力脉动.蒙皮振动使流体更加靠近壁面运动,大尺度的层流分离现象得到有效抑制. 相似文献
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本文对机翼外挂系统颤振的半主动抑制实验进行了研究分析,在引入电磁阻尼器对风振控制的同时,根据增益调度控制原理设计并制造了控制系统,在风洞实验中实现了电磁阻尼器对系统的颤振半主动抑制,为颤振抑制的实现又提供了一种实验的方法。 相似文献
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S. V. Zhigulev M. N. Kogan A. P. Kuryachii V. M. Litvinov A. A. Uspenskii 《Fluid Dynamics》2008,43(5):718-724
The effect of mini-flaps on the flow pattern in the near vortex wake behind a model swept half-wing is investigated. The distributions of the time-average flow velocity were measured in a subsonic wind tunnel, in a section normal to the freestream velocity vector located at a distance of 3.8 wing half-spans from its trailing edge. When mini-flaps are mounted on both upper and lower wing surfaces, two vortices (tip and auxiliary) of the same sign are observable in the above-mentioned flow section; they are separated by an extended region of vorticity of the opposite sign. The model angle-of-attack effect on the intensities of the tip and auxiliary vortices is estimated. 相似文献
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Simulation of the aerodynamics of buildings and structures by means of the closed vortex loop method
Problems of the numerical simulation of the air flow past buildings and structures are considered using the closed vortex loop method. A mathematical model, based on the vortex approach, of the time-dependent ideal incompressible fluid flow past a system of bodies is proposed. A numerical scheme for solving the problem and an algorithm for calculating the distributed wind loads over the body surface are outlined. An example of calculating the aerodynamic loads is given for a real building and the results are compared with the known results of testing a model of the building in a wind tunnel. An example of the calculation and analysis of the wind distribution over a system of several buildings is also presented. 相似文献
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Flow past model wings is experimentally investigated in a subsonic wind tunnel at large angles of attack at which the laminar boundary layer separates near the leading edge of the wing (flow stall). The object of the study was the flow structure within the separation zone. The carbon-oil visualization of surface streamlines used in the experiments showed that in the separation zone there exist one or more pairs of large-scale vortices rotating in the wing plane. Certain general properties of the vortex structures in the separation zone are found to exist, whereas the flow patterns may differ depending on the model aspect ratio, the yaw angle, and other factors. 相似文献
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The construction of three-dimensional surface flow fields is an extremely difficult task owing largely to the fragmented information
available in the form of 2D images. Here, the method of photogrammetric resection based on a comprehensive camera model has
been used to map oil flow visualization images on to the surface grid of the model. The data exported in the VRML format allow
for user interaction in a manner not possible with 2D images. The technique is demonstrated here using the surface oil flow
visualization images of a simplified landing gear model at low speed in a conventional wind tunnel without any specialized
rigs for photogrammetry. The results are not limited to low-speed regimes and show that this technique can have significant
impact on understanding the flow physics associated with the surface flow topology of highly three-dimensional separated flows
on complex models. 相似文献
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Reynolds number effects on the vortical-flow structure generated by a double-delta wing 总被引:1,自引:0,他引:1
An experimental investigation of the high-incidence vortical flowfield over a 76/40° double-delta wing model with sharp leading
edges was conducted in the Naval Postgraduate School water tunnel facility at three nominal flow Reynolds numbers of 15000,
45000, and 75000 (based on centerline chord). Extensive flow visualization studies were performed with the dye-injection technique,
followed by laser Doppler velocity measurements. The primary objective of this investigation was the determination of the
influence of Reynolds number on vortex interactions/trajectories, and breakdown. It was found that there is a significant
influence of Reynolds number. Specifically, with the increase of flow Reynolds number the strake and wing vortex trajectories
tend to move outboards and closer to the model surface, and the vortex breakdown location moves forwards toward the apex of
the model. The intertwining or coiling-up feature of the vortex interaction phenomenon becomes less dominant and disappears
altogether at high Reynolds numbers. These trends in the vortex interaction and bursting data are found to be in good agreement
with previous wind tunnel data.
Received: 26 March 1998/Accepted: 2 February 1999 相似文献
19.
Static Finite Element Validation of a Flexible Micro Air Vehicle 总被引:1,自引:0,他引:1
The flexible-wing approach has proven to be a successful method for designing micro air vehicles. The wing’s passive deformation
under wind loads can allow for gust rejection, delayed stall, or improved longitudinal stability. As such, an accurate structural
model of the flexible wing can provide greater understanding of the aforementioned phenomena. This paper seeks to formulate
a static finite element wing model, with a particular emphasis on accuracy. The wing is broken into three different types
of elements: beams, plates, and membranes. Individual element types are characterized and validated by constructing simple
structures from the appropriate material, and then comparing experimental and numerical deformation fields. Experimental results
are found through a visual image correlation system. The elements are then combined to form the complete wing model, which
is also validated through experiments. The resulting finite element model is found to be very accurate, able to predict the
complicated structural response of a composite wing. Due to observations made during standard wind tunnel testing, the structural
response of a typical membrane MAV wing in steady level pre-stall flight is thought to be quasi-static. As such, the finite
element model formulated in this work will be indispensable towards future numerical static aeroelastic optimization research
efforts aimed at improving the efficiency, agility, and sensitivity of practical micro air vehicles. 相似文献
20.
The limit cycle oscillation (LCO) behaviors of control surface buzz in transonic flow are studied. Euler equations are employed to obtain the unsteady aerodynamic forces for Type B and Type C buzz analyses, and an all-movable control surface model, a wing/control surface model and a three-dimensional wing with a full-span control surface are adopted in the study. Aerodynamic and structural describing functions are used to deal with aerodynamic and structural nonlinearities, respectively. Then the buzz speed and buzz frequency are obtained by V-g method. The LCO behavior of the transonic control surface buzz system with linear structure exhibits subcritical or supercritical bifurcation at different Mach numbers. For nonlinear structural model with a free-play nonlinearity in the control surface deflection stiffness, the double LCO phenomenon is observed in certain range of flutter speed. The free-play nonlinearity changes the stability of LCOs at small amplitudes and turns the unstable LCO into a stable one. The LCO behavior is dominated by the aerodynamic nonlinearity for the case with large control surface oscillation amplitude but by the structural nonlinearity for the case with small amplitude. Good agreements between LCO behaviors obtained by the present method and available experimental data show that our study may help to explain the experimental observation in wind tunnel tests and to understand the physical mechanism of transonic control surface buzz. 相似文献