等离子体流动控制研究进展与展望

等离子体流动控制是基于等离子体气动激励的新型主动流动控制技术,具有响应时间短、激励频带宽等显著技术优势,在改善飞行器/发动机空气动力特性方面具有广阔的应用前景,已成为国际上等离子体动力学与空气动力学交叉领域的前沿研究热点。鉴于此,从介质阻挡放电(DBD)、电弧放电等离子体气动激励特性,等离子体气动激励抑制流动分离、控制附面层、控制激波与激波/附面层干扰、控制压气机与涡轮内部流动、控制管道流动和飞行控制等方面,综合评述了国际上等离子体流动控制的研究进展情况;从创新等离子体气动激励方式,揭示等离子体气动激励与复杂流动的非定常耦合机制,突破等离子体流动控制系统关键技术等方面,对未来的发展进行展望。     

Adaptive flow control of low-Reynolds number aerodynamics using dielectric barrier discharge actuator

Aerodynamic performance of low-Reynolds number flyers, for a chord-based Reynolds number of 10⁵ or below, is sensitive to wind gusts and flow separation. Active flow control offers insight into fluid physics as well as possible improvements in vehicle performance. While facilitating flow control by introducing feedback control and fluidic devices, major challenges of achieving a target aerodynamic performance under unsteady flow conditions lie on the high-dimensional nonlinear dynamics of the flow system. Therefore, a successful flow control framework requires a viable as well as accessible control scheme and understanding of underlying flow dynamics as key information of the flow system. On the other hand, promising devices have been developed recently to facilitate flow control in this flow regime. The dielectric barrier discharge (DBD) actuator is such an example; it does not have moving parts and provides fast impact on the flow field locally. In this paper, recent feedback flow control studies, especially those focusing on unsteady low-Reynolds number aerodynamics, are reviewed. As an example of an effective flow control framework, it is demonstrated that aerodynamic lift of a high angle-of-attack wing under fluctuating free-stream conditions can be stabilized using the DBD actuator and an adaptive algorithm based on general input–output models. System nonlinearities and control challenges are discussed by assessing control performance and the variation of the system parameters under various flow and actuation conditions. Other fundamental issues from the flow dynamics view point, such as the lift stabilization mechanism and the influence on drag fluctuation are also explored. Both potentiality and limitation of the linear modeling approach are discussed. In addition, guidelines on system identification and the controller and actuator setups are suggested.     

低速翼型分离流动的等离子体主动控制研究

为了研究等离子体激励器的放电形式及其诱导气流的规律,以及翼型迎角、自由来流速度分别对翼型流动分离抑制效果的影响。在低速、低雷诺数条件下利用介质阻挡放电等离子体激励器对NACA0015翼型进行了主动流动控制研究。结果表明：介质阻挡放电的形式为丝状放电;等离子体激励器诱导气流的方向由裸露电极指向覆盖电极,由电极的布置方式决定,与接线方式无关;当来流速度为25m／s,雷诺数为2．03×10^5时,等离子体气动激励可以有效地抑制翼型吸力面的流动分离,翼型最大升力系数增大约为9．7％,翼型l临界失速迎角由17．5°增大到20．5°;翼型失速延迟的真正原因并非单纯的气流加速;等离子体激励器的作用效果随着来流速度的提高而减弱,研究非定常激励或等离子体激励器与流场之间的耦合效应,也许更加具有潜力。     

Experimental Investigation into Characteristics of Plasma Aerodynamic Actuation Generated by Dielectric Barrier Discharge

This article carries out synthetic measurements and analysis of the characteristics of the asymmetric surface dielectric barrier discharge plasma aerodynamic actuation.The rotational and vibrational temperatures of an N2 (C3Пu) molecule are measured in terms of the optical emission spectra from the N2 second positive system.A simplified collision-radiation model for N2(C) and N2+(B) is established on the basis of the ratio of emission intensity at 391.4 nm to that at 380.5 nm and the ratio of emission intensity at 371.1 nm to that at 380.5 nm for calculating temporal and spatial averaged electron temperatures and densities.Under one atmosphere pressure,the electron temperature and density are on the order of 1.6 eV and 1011cm-3 respectively.The body force induced by the plasma aerodynamic actuation is on the order of tens of mN while the induced flow velocity is around 1.3m/s.Starting vortex is firstly induced by the actuation;then it develops into a near-wall jet,about 70 mm downstream of the actuator.Unsteady plasma aerodynamic actuation might stimulate more vortexes in the flow field.The induced flow direction by nanosecond discharge plasma aerodynamic actuation is not parallel,but vertical to the dielectric layer surface.     

双旋翼微型飞行器的非定常气动特性

发展了一种基于计算流体力学(CFD)的非定常气动特性预测方法,计算方法包括了动量源模型、预处理方法、非结构嵌套网格和Spalart-Allmaras(S-A)湍流模型等技术.通过计算悬停Caradonna-Tung算例和俯仰振荡NACA0012算例,验证了计算方法模拟双旋翼微型飞行器动态流场的有效性.数值模拟了双旋翼微型飞行器动态流场,给出了非定常气动系数的迟滞曲线,分析了缩减频率、前飞速度和螺旋桨转速对非定常气动特性的影响.计算结果表明:力矩系数迟滞效应随缩减频率、前飞速度和螺旋桨转速增大而增大,升力系数迟滞效应随缩减频率和前飞速度增大而增大,但基本不随螺旋桨转速变化而变化.      

翼型动态失速等离子体流动控制试验

针对动态失速引起的翼型气动性能恶化的问题,利用小型化的激励电源和介质阻挡放电等离子体激励器,借助动态压力测量和外触发式粒子图像测速（PIV）等手段开展了翼型动态失速等离子体流动控制试验研究。结果表明,等离子体气动激励能够有效控制翼型动态失速,改善平均气动力,提高翼型气动效率,减小气动力随迎角变化的迟滞区域。等离子体诱导出前缘附近的贴体翼面涡,促进分离流再附;增加了上翼面0.2~0.4弦长区域的吸力,减小了升力系数功率谱密度（PSD）分布的二、三、四阶能量幅值,在研究工况下实现了平均升力系数增加7.1%、失速迎角推迟1.3°和迟滞区域减小4.5%的明显控制效果;4°~9°迎角段,等离子体使得翼型平均阻力系数减小40%。此外,振荡频率增加使翼型绕流的非定常性增强,较高雷诺数下的翼型动态分离涡更加难以被抑制,均需要增加等离子体激励强度才能达到较好的控制效果。     

等离子体气动激励抑制翼型失速分离的仿真研究

通过求解表面放电的二维流体体力模型,建立了翼型等离子体流动控制的数学模型,得到等离子体气动激励诱导的体力和热量分布,与Navier-Stokes方程耦合求解.进行了低雷诺数条件下,等离子体气动激励抑制NACA0009翼型失速分离的数值仿真研究,研究了等离子体激励的强度、激励电极数目和激励位置对流动分离抑制和翼型升阻特性的影响.在雷诺数为58000、攻角为24°的情况下,施加等离子体激励后,升力系数由0.7449增大到1.2404;阻力系数由0.4012减小到0.3503.      

介质阻挡放电对增升装置气动性能的影响

增升装置是传统构型飞机的重要组成部分,对飞行器气动性能有重要影响。将高效、简便、节能的介质阻挡放电(Dielectric Barrier Discharge,DBD)等离子体激励器布置在增升装置附近,通过对流场进行控制来达到提高增升装置气动性能的作用。选取二维翼型GAW-1及其29%襟翼作为研究对象,在分析基础流场的基础上,固定激励器放电频率等参数不变,将单级介质阻挡放电激励器放置在几个不同位置,用数值模拟的方法研究其对翼型总体气动特性的影响。仿真结果表明,主翼上表面后缘处的激励器增升效果最好,增升达12.8%且将失速迎角推迟约2°,主翼下表面后缘的升阻比增加可达15%。     

射频介质阻挡放电改善NACA 0015翼型气动性能的实验

介质阻挡放电(DBD)均匀稳定、易于敷设,是机翼/翼型等离子体流动控制(PFC)中最常用的激励方式。射频介质阻挡放电激励频率高、放电功率大,且能在流场中产生明显的加热,应用潜力大。采用射频电源驱动DBD激励器产生等离子体,分析放电的体积力、热特性和诱导流场特性,开展了射频介质阻挡放电改善NACA 0015翼型气动性能的实验,研究了占空比、调制频率、载波频率和电源功率等参数对流动控制效果的影响规律。结果表明:射频等离子体激励的体积力效应随激励电压的增大而增加;射频等离子体激励产生的热量在诱导的流场中进行传导,加速流场;当来流速度为20m/s,Re=3.36×10~5时,在翼型前缘施加激励,使翼型临界失速迎角推迟1°,最大升力系数增大6.43%,且在过失速迎角下仍具有流动控制效果,使升力下降变缓;调制频率越大,控制效果越好;存在最佳占空比、载波频率和功率,占空比对流场控制效果的影响最显著,最佳占空比、载波频率和功率分别为20%,460kHz和50W。射频等离子体激励以体积力效应、热效应和诱导壁面射流改善失速流场,使得NACA0015翼型气动性能极大改善,流动分离得到有效控制。     

纳秒脉冲等离子体激励器用于圆柱高速流动控制的数值模拟

利用数值模拟,研究了纳秒脉冲介质阻挡放电（NS-DBD）等离子体激励器在圆柱高速流动控制中的应用。首先,研究了单电极NS-DBD等离子体激励器在静止空气中放电后的流场特性。研究表明在介质阻挡放电形成的等离子体区域,有局部能量快速注入,放电结束5 μs后在上极板后端点位置形成了一个局部温度高达900 K的热点,由此引发很强的压力扰动,形成以上极板后端点位置为中心,扩散速度约为声速的半圆形压缩波。在此基础上,通过数值模拟研究了NS-DBD等离子体激励器布置在直径为6 mm的圆柱上,来流马赫数为Ma_∞=4.6时,对圆柱脱体激波的控制作用。研究表明介质阻挡放电形成的半圆形压缩波对于脱体激波有很强的干扰作用,激波距离增加了15.7%,激波强度也有相应的减弱,导致阻力减少了13%。     

大型水陆两栖飞机吹气襟翼设计与分析验证

针对大型水陆两栖飞机的使用特点和指标要求,以原型机翼为基础,重点开展机翼附面层控制增升装置设计技术研究,设计了附面层控制的吹气襟翼方案.采用计算流体动力学方法作为初步设计的评估手段,全面分析评估了设计方案的气动力特性和流场结构,最后通过风洞试验验证了该方案的增升效果.结果显示该设计方案在较宽的吹气动量系数范围内,最大升力系数均有不同程度的增幅,在吹气动量系数约为0.2左右时,获得最大的升力系数增量约为1.0,按照原型机的滑流影响规律推算,当采用吹气襟翼的主动流动控制方案后,起降速度能下降约30%,达到了设计指标.      

超声速非平衡电离磁流体动力技术实验系统

介绍了超声速非平衡电离磁流体动力技术实验系统的设计思想和组成,设计、制作了马赫数为3.5的吸气式双喉道风洞,采用以陶瓷板为阻挡介质的电容耦合射频阻挡放电,实现了超声速流场中大体积、连续、稳定、均匀等离子体的产生.主要结论有:实验测试风洞稳定工作时间为18s,稳定运行时实验段静压为650Pa;电容耦合射频放电典型工作状态下,通过伏安诊断法测出超声速条件下等离子体的电导率为1.27×10-3S/m.      

毫秒脉冲等离子体激励改善飞翼的气动性能实验

在来流速度为30m/s时,进行了毫秒脉冲介质阻挡放电等离子体激励改善飞翼气动性能的风洞实验.等离子体激励器布置在飞翼前缘,峰峰值电压为9.5kV时,放电的脉冲能量在0.1mJ/cm量级.通过六分量测力天平测力研究了脉冲激励频率和占空比对升/阻力系数、升阻比和俯仰力矩系数的作用效果.结果表明:等离子体激励可以有效改善飞翼大攻角气动特性;在最佳无量纲脉冲激励频率F+≈1时,临界失速迎角由14°提高到17°,最大升力系数提高10%;占空比对流动控制效果影响较大,减小占空比可以降低能耗,实验中最佳占空比为5%;俯仰力矩系数的变化表明施加等离子体激励改善了飞翼纵向静稳定性.      

SDBD plasma enhanced aerodynamics: concepts,optimization and applications

This paper provides an overview of the physics and design of single dielectric barrier discharge (SDBD) plasma actuators for enhanced aerodynamics in a variety of applications. The actuators consist of two electrodes, one exposed to the air and the other covered by a dielectric material. The electrodes are supplied with an ac voltage that at high enough levels, causes the air over the covered electrode to ionize. The ionization of the air is a dynamic process within the ac cycle. The ionized air, in the presence of the electric field produced by the electrode geometry, results in a body force vector that acts on the ambient air. The body force is the mechanism for active aerodynamic control. The body force per unit volume of plasma has been derived from first principles and implemented in numerical flow simulations. This utilizes models for the time and space dependence of the air ionization on the input voltage amplitude, frequency, electrode geometry and dielectric properties that have been developed and bench-marked with experiments. The experiments and model suggest approaches that can maximize the performance of the plasma actuators. A sample implementation of an actuator model in a numerical flow simulation consisting of leading-edge separation control on an airfoil along with an experimental benchmark is then presented.     

低速三角翼纳秒脉冲等离子体激励实验

在30m/s来流速度下,进行了纳秒脉冲介质阻挡放电等离子体气动激励改善47°后掠角钝前缘三角翼气动特性的测力实验.为寻求优化的激励位置,实验研究了5种不同激励位置的流动控制效果.实验结果表明:激励位置对流动控制效果有决定性影响,位于三角翼前缘的等离子体气动激励能有效改善三角翼的气动特性,推迟失速,而上翼面不同展向位置的等离子体气动激励的流动控制效果十分微弱;激励频率是流动控制效果的重要影响因子,激励电压峰峰值为13kV时,激励频率为200Hz下的流动控制效果最好,在迎角30°时可使升力系数由1.31增大到1.44,增大9.6%,升阻比提高3.3%.     

Aerodynamic performance enhancement of a flying wing using nanosecond pulsed DBD plasma actuator

Experimental investigation of aerodynamic control on a 35 swept flying wing by means of nanosecond dielectric barrier discharge(NS-DBD) plasma was carried out at subsonic flow speed of 20–40 m/s, corresponding to Reynolds number of 3.1 · 105–6.2 · 105. In control condition, the plasma actuator was installed symmetrically on the leading edge of the wing. Lift coefficient, drag coefficient, lift-to-drag ratio and pitching moment coefficient were tested with and without control for a range of angles of attack. The tested results indicate that an increase of 14.5% in maximum lift coefficient, a decrease of 34.2% in drag coefficient, an increase of 22.4% in maximum lift-to-drag ratio and an increase of 2 at stall angle of attack could be achieved compared with the baseline case. The effects of pulsed frequency, amplitude and chord Reynolds number were also investigated.And the results revealed that control efficiency demonstrated strong dependence on pulsed frequency. Moreover, the results of pitching moment coefficient indicated that the breakdown of leading edge vortices could be delayed by plasma actuator at low pulsed frequencies.     

等离子体激励器对微型飞行器横航向气动力矩控制的实验研究

在前期等离子体激励器基本流场特性研究的基础上,将等离子体激励器应用于微型飞行器(MAV)进行气动控制。当来流速度为9.1 m/s时,在微型飞行器机翼吸力面非对称布置不同的单介质阻挡放电(SDBD)等离子体激励器,通过对未施加激励的偏航、滚转力矩曲线和施加激励的偏航、滚转力矩曲线进行对比,发现横航向气动力距发生很大的改变,可以实现对横航向气动力矩的控制。在此基础上,采用图像测速(PIV)技术,对机翼背风面的流场进行研究,分析产生横航向控制力矩的流动机理。通过改变激励器的输入电压、占空比和调制频率,实现对横航向气动力矩的比例控制。     

基于CFD/CSD紧耦合的旋翼翼型气弹分析

采用CFD/CSD（计算流体力学/计算结构力学）紧耦合的方法,以Fluent软件作为主控平台,通过UDF（用户自定义函数）及I/O（输入/输出）文件读写的方式实现结构响应和气动载荷的数据交换,耦合求解了旋翼桨叶剖面的气动力和振动响应.在此基础上研究旋翼桨叶剖面在变距、沉降（挥舞）和周期交变来流条件下的气动特性和振动响应特性.结果表明:桨叶剖面在轻失速情况下,气动载荷周期性比较好,表现出光滑的迟滞环曲线,结构沉降响应也表现出光滑的周期性现象,扭转响应出现局部轻微振荡.深失速情况下,气动载荷及结构响应都表现出强烈的非线性振荡,高频成分较为明显.      

高超声速复杂气动问题数值方法研究进展

高超声速流场具有复杂流动特征,其中真实气体效应、磁流体干扰效应和力热结构耦合效应等对气动力分析产生了重要影响。将流体力学研究扩展到分子动力学、电磁流体力学以及流固耦合等交叉学科领域,这给数值模拟方法带来了巨大挑战。针对高超声速气动力/热分析的热点问题,重点关注高温效应与低密度流动效应、磁流体干扰效应和力热结构耦合效应等,结合算例分析了相应的数值求解技术;在气动热方面主要比较了3类求解方法(纯工程方法、纯数值方法和基于Prandtl边界层理论的方法),并给出了相应算例;对于气动力/热/结构耦合问题,从耦合模型及耦合计算方法两方面开展了分析。最后指出了高超声速复杂气动问题数值求解技术未来需重点关注的几个方面。     

CFD/CSD方法分析动力效应对民机气动特性影响

基于Reynolds average Navier-Stockes(RANS)的三维Navier-Stokes流场控制方程耦合结构静力学方程时域分析方法,研究了带有发动机的民用飞机其动力效应对全机气动性能的影响。首先采用数值方法对发动机进排气边界条件进行了模拟,分析了带动力的涡扇发动机模型的流场,并将计算结果与实验进行比较,验证边界条件处理的准确性;以此为基础,考虑结构弹性变形,采用计算流体动力学/计算结构动力学(CFD/CSD)耦合的方法,分别对通气和带动力的翼吊发动机全机的气动性能进行了研究。结果表明:基于通气构型预测的升阻力系数,气动载荷和压心位置与考虑动力效应后的计算结果存在明显不同。弹性变形又会加剧这一差异,使得全机的升阻比下降约12.6%,升力系数下降约8.9%,压心位置后移。数值算例显示,在靠近发动机区域气动载荷受动力效应影响显著,远离该区域,弹性变形效应占主要影响因素,因此在进行带动力效应的民机气动性能分析时,考虑弹性变形的影响是十分必要的。