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《Aerospace Science and Technology》2006,10(5):394-400
In the first part of this contribution [G. Godard, M. Stanislas, Control of a decelerating boundary layer. Part 1: Optimization of passive vortex generators, Aerospace Sci. Technol. 10 (3) (2006) 181–191], an optimization of passive vortex generators was performed in an adverse pressure gradient boundary layer. The model used was a bump in a boundary layer wind tunnel, which mimics the adverse pressure gradient on the suction side of an airfoil at the verge of separation. The present contribution describes the next step of the study: a test campaign was performed in the same facility to optimize slotted jets devices with both continuous and pulsed blowing. The optimization was done using hot film shear stress probes. The results show quantitatively the improvement brought by the slotted jets devices in terms of skin friction increase. They also show that the tested devices are less effective than equivalent passive devices. 相似文献
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An investigation on the viability of pulsed jets as active vortex generator devices was conducted. The devices were installed and tested on an adverse pressure gradient turbulent boundary layer designed to simulate the suction side of a conventional aircraft wing. Both co-rotating and counter-rotating jet geometries were used. The duty cycle and frequency of pulsation were varied and their effects were investigated by measuring the skin friction gains at a predefined location (the location of the minimum skin friction for the un-actuated situation) on the adverse pressure gradient turbulent boundary layer. Pulsing the jets proved to be successful in increasing the wall skin friction and therefore potentially delaying separation. The improvements in wall shear stress were approximately proportional to the duty cycle. The frequency of jet pulsation was found to be important for attaining optimal gains, however no clear relationship between frequency and shear stress gain was observed. Phase averaged wall shear stress measurements far downstream of actuation indicate that quasi-steady structures are introduced by the vortex generators when actuating with a sufficiently high pulse frequency. In this situation interactions between successive structures produced by the jets were likely to be occurring. 相似文献
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《Progress in Aerospace Sciences》2002,38(4-5):389-420
An in-depth review of boundary-layer flow-separation control by a passive method using low-profile vortex generators is presented. The generators are defined as those with a device height between 10% and 50% of the boundary-layer thickness. Key results are presented for several research efforts, all of which were performed within the past decade and a half where the majority of these works emphasize experimentation with some recent efforts on numerical simulations. Topics of discussion consist of both basic fluid dynamics and applied aerodynamics research. The fluid dynamics research includes comparative studies on separation control effectiveness as well as device-induced vortex characterization and correlation. The comparative studies cover the controlling of low-speed separated flows in adverse pressure gradient and supersonic shock-induced separation. The aerodynamics research includes several applications for aircraft performance enhancement and covers a wide range of speeds. Significant performance improvements are achieved through increased lift and/or reduced drag for various airfoils—low-Reynolds number, high-lift, and transonic—as well as highly swept wings. Performance enhancements for non-airfoil applications include aircraft interior noise reduction, inlet flow distortion alleviation inside compact ducts, and a more efficient overwing fairing. The low-profile vortex generators are best for being applied to applications where flow-separation locations are relatively fixed and the generators can be placed reasonably close upstream of the separation. Using the approach of minimal near-wall protuberances through substantially reduced device height, these devices can produce streamwise vortices just strong enough to overcome the separation without unnecessarily persisting within the boundary layer once the flow-control objective is achieved. Practical advantages of low-profile vortex generators, such as their inherent simplicity and low device drag, are demonstrated to be critically important for many applications as well. 相似文献
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为了研究涡发生器(VGs)间距λ对控制边界层分离效果的影响,选取了4种涡发生器间距,λ/H(H为涡发生器高度)分别为5,7,9,11.采用大涡模拟(LES)方法对带逆压梯度的平板边界层分离流动及VGs控制分离流动进行了数值模拟.分析了有无VGs控制时,湍流场中大尺度相干结构及其演化规律,分别从旋涡间距、边界层内流体动能、压差损失等方面考察了VGs间距对控制流动分离效果的影响.研究结果表明当λ/H为5时,VGs间距过小抑制了旋涡的展向发展,λ/H为9,11时,VGs间距过大边界层内流体动能偏低,当间距λ/H为7时流动控制效果更优,此时计算域压差损失最小,相比较无VGs控制时,压差损失降低了30.95%. 相似文献
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《Aerospace Science and Technology》2006,10(3):181-191
The control of boundary layer separation on the suction side of an airfoil at high angle of attack has been renewed by the possibilities of active control. Nevertheless, such an active control needs a deep understanding of the flow to manipulate and of the actuating flow, both being 3D and unsteady. For that purpose, a model experiment has been designed in the frame of a coordinated European project called AEROMEMS, with a simpler (2D) geometry and with a dilatation of the scales in order to be able to characterize the actuation flow. This model is a bump in a boundary layer wind tunnel, which mimics the adverse pressure gradient on the suction side of an airfoil at the verge of separation. The present contribution describes preliminary tests done to optimize standard passive devices before testing active systems. The optimization was done with hot film shear stress probes, the characterization with hot wire anemometry and PIV. The results show quantitatively the improvement brought by the passive devices in terms of skin friction. They also show the mechanism which is at the origin of this improvement. The next step of the project is to replace passive devices by synthetic jets. 相似文献
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本文介绍了一种新型的凹型面埋入式涡流发生器的工作机理。并介绍在一个小宽高比二元单边凹壁亚声扩压壁前段出现气流分离,角落区域有倒流的情况下,采用适当几何参数的该型式涡流发生器大大减小分离区的范围,从而提高了扩压器静压恢复系数和减小总压损失系数的试验结果。 相似文献
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本文介绍了在一个大宽高比大扩压角二元亚音扩压器中采用适当几何参数的凹型面埋入式涡流发生器有效地控制扩压壁和角落区域分离流的试验结果。并分析了该型式涡流发生器主要几何参数对扩压器性能的影响。还对该型式涡流发生器与常规翼型式涡流发生器进行了比较。 相似文献
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针对安装在大后掠角机翼上的涡流发生器控制流动分离的问题,采用雷诺平均纳维 斯托克斯 (RANS) 方程以及剪切应力传输 (SST) 湍流模型,通过搭接网格技术,对带有涡流发生器 (VG) 的大后掠角机翼进行数值模拟,分析VG的安装位置对大后掠角机翼边界层分离的控制机理及气动特性影响。研究发现VG的作用仅仅在其周边边界层内部区域,影响范围小,在弦线方向安装VG存在最佳布置位置。VG必须安装在靠近气流将要分离的高能量区域,才能有效的抑制气流分离,达到增升减阻的效果。 相似文献
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射流式旋涡发生器对弯曲扩压叶栅流场的影响 总被引:1,自引:1,他引:0
数值模拟了射流式旋涡发生器对于大折转角弯曲扩压叶栅端壁流场性能的影响.结果表明:该研究的几种具有不同参数的射流式旋涡发生器都能使弯曲叶片损失降低,正弯和反弯叶片损失减小程度最大分别达2.5%和8.8%.射流除了可为端壁附近边界层中的低能流体提供动量之外,还可以在流道中产生与通道涡旋向相反、强度相当的流向旋涡挤压通道涡,使其向远离吸力面的方向偏转,该流向旋涡在距离叶片前缘0.6倍轴线弦长附近消失.对正弯叶片,吸力面上的流动分离现象基本消失,对于反弯叶片,极大程度上降低了吸力面集中脱落涡的强度.此外,射流作用使得弯曲叶片的负荷和折转能力均增加. 相似文献
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高超声速进气道强制转捩流动的大涡模拟 总被引:1,自引:0,他引:1
吸气式高超声速飞行器常在进气道边界层内布置粗糙颗粒或涡流发生器强制流动转捩为湍流以确保发动机正常启动。为了清晰认识强制转捩过程,采用隐式大涡模拟方法,对强制转捩问题开展了数值模拟研究。针对钻石形和斜坡形涡流发生器,计算得到涡流发生器诱导的流动结构,显示出强制转捩流动由涡流发生器产生的反向旋转流向涡对主导。扰动沿流向增长和发展,导致流向涡对以偶模式或奇模式失稳,偶模式失稳产生对称形式的涡对破碎,而奇模式失稳则导致非对称(弯曲)形式的涡对破碎。流向涡对破碎后产生一系列发卡涡并最终促使边界层转捩为湍流。最后就计算网格和数值耗散对隐式大涡模拟结果的影响以及计算的收敛性进行了讨论。 相似文献
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双模态超燃冲压发动机由于压力扰动可能发生不起动现象,造成推力严重下降,对飞行稳定性与飞行安全具有很强的破坏性.不起动初始阶段主要受到激波与边界层相互作用引起的流动分离影响,希望通过控制分离达到改善流动的目的.采用5阶特征型WENO(weighted essentially non-oscillator)格式与3阶TVD(total variation diminishing)型Runge-Kutta(R-K)格式的高精度数值方法,求解三维Navier-Stokes(N-S)方程,研究与分析了凸起物和被动吹吸两种被动控制方法对激波与边界层相互作用导致的高超声速流动分离现象的控制效果.结果表明:凸起物通过诱导流向涡形成,改变空间压力分布,减弱二次分离,影响分离结构;吹吸方式的被动控制技术通过平衡分离区与再附区之间的高低压差,降低逆压梯度,使压力分布与分离区域发生改变. 相似文献
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2.4m跨声速风洞槽壁试验段调试及流场校测 总被引:1,自引:0,他引:1
介绍了新研制的2.4m跨声速风洞槽壁试验段调试情况及流场校测结果。结果表明:该试验段边界层厚度、消波特性等满足使用需求,具有较大的流场均匀区,在M数为0.30~1.00范围内的核心流场M数分布均方根偏差满足GJB1179-91高速风洞与低速风洞流场品质规范合格指标要求,部分马赫数的均方根偏差达到或接近先进指标要求,可投入型号试验。槽壁试验段的成功研制提高了2.4m跨声速风洞承担大型飞机试验任务的能力,在中国大型飞机工程气动设计中将发挥重要的平台作用。 相似文献
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一种亚声速进气道出口流场存在较严重的总压畸变,为改善其出口流场品质,抑制总压畸变,首先分析了引起总压畸变的原因,即进气道扩张段内边界层发生分离;其次提出了在进气道内安装叶片式涡流发生器的流动控制方法,并进行了仿真验证;最后进行了进气道缩比模型的风洞试验。试验结果表明,在进气道设计马赫数(0.65)和非设计马赫数(0.21)条件下,安装叶片式涡流发生器后,在流量系数0.4~0.85范围内,进气道出口流场的综合畸变指数分别平均降低14.7%和23.8%,因此验证了流动控制方法的有效性。 相似文献
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《中国航空学报》2020,33(1):73-87
In order to improve the control ability of synthetic jets in compressible boundary layer, a novel control method based on dual synthetic cold/hot jets coupled control of velocity profile and temperature profile was proposed. As fundamental investigations on the effects of synthetic jet temperature on the jet behavior and flow field characteristics were essentially necessary, preliminary numerical simulations were conducted to study the influence of temperature (200 K and 400 K) on the flow field characteristics of synthetic jets using Large Eddy Simulations (LES) model. Time-averaged flow fields showed that different temperatures led to variable behavior of two strands of jets. For dual synthetic cold jets, a potential-core arose apparently with its height ranging from 0.01 to 0.03 m, while for dual synthetic hot jets, two strands of jets emerged downstream. The modal decomposition of instantaneous flow fields had been done using both Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD). Various modes showed different characteristics of the flow fields. As the POD method focuses on the energy of flow while the DMD method focuses on the frequency, the first two modes had many similarities, but the third and fourth modes demonstrated completely different vortex structures. The current researches play a role of preliminary investigations for further and comprehensive exploration of novel flow control measures in global velocity field. 相似文献
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分别对收缩通道、扩张通道和直通道中亚声速主流条件下的气膜冷却进行数值模拟,对比分析了不同主流压力梯度、次流吹风比条件下的主流和次流流场、温度场特征。研究结果表明:引起气膜冷却效率变化和不同发展趋势的因素可归结为主流边界层厚度、主次流自由剪切混合程度、肾形涡的强度和位置等因素。相对于零压力梯度的主流条件,在吹风比较小(M=0.25)的情况下,主流的逆压力梯度一方面增厚边界层、增强了气膜射流对主流的穿透,另一方面减小了肾形涡的强度,综合作用的结果是气膜平均冷却效率提高了4.91%。在吹风比较大(M=2)的情况下,主流的顺压力梯度扼制主流边界层的发展、抑制气膜射流的穿透能力,降低肾形涡涡核的位置,从而提高气膜冷却效率达17.40%。 相似文献
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研究滑流对埋入式进气道性能的影响机理对于发动机的稳定性具有重要意义。针对某型涡桨发动机 滑油散热器进排气道系统,基于 CFD技术建立系统的螺旋桨滑流与滑油散热器内流一体化数值模拟方法,进 行考虑滑流影响的滑油散热系统埋入式进气道气动设计仿真分析;针对埋入式进气道由于吸入边界层低能气 流导致通过散热器流量低的问题,设计4组涡流发生器进行主动流动控制。结果表明:滑流使得进气道中的气 流偏离,难以形成稳定漩涡,容易发生流动分离;而合理设计的涡流发生器可以有效改善埋入式进气道内流场 特性,并使通过散热器的流量提高12%。 相似文献