Dynamic Stall on High-Lift Airfoil 30P30N in Ground Proximity

Computational prediction of stall aerodynamics in free air and in close proximity to the ground considering the 30P30N three-element high-lift configuration is carried out based on CFD simulations using the OpenFOAM code and Fluent software. Both the attached and separated flow regimes are simulated using the Reynolds Averaged Navier-Stokes (RANS) equations closed with the Spalart-Allamaras (SA) turbulence model for static conditions and pitch oscillations at Reynolds number, Re = 5 x 106 and Mach number, M = 0.2. The effects of closeness to the ground and dynamic stall are investigated and the reduction in the lift force in close proximity to the ground is discussed.

Airfoil friction drag reduction based on grid-type and super-dense array plasma actuators

To improve the cruise flight performance of aircraft, two new configurations of plasma actuators(grid-type and super-dense array) were investigated to reduce the turbulent skin friction drag of a low-speed airfoil. The induced jet characteristics of the two actuators in quiescent air were diagnosed with high-speed particle image velocimetry(PIV), and their drag reduction efficiencies were examined under different operating conditions in a wind tunnel. The results showed that the grid-type plasma actuator was capable of producing a wall-normal jet array(peak magnitude: 1.07 m/s) similar to that generated in a micro-blowing technique, while the superdense array plasma actuator created a wavy wall-parallel jet(magnitude: 0.94 m/s) due to the discrete spanwise electrostatic forces. Under a comparable electrical power consumption level,the super-dense array plasma actuator array significantly outperformed the grid-type configuration,reducing the total airfoil friction drag by approximately 22% at a free-stream velocity of 20 m/s.The magnitude of drag reduction was proportional to the dimensionless jet velocity ratio(r), and a threshold r = 0.014 existed under which little impact on airfoil drag could be discerned.

Influence of Flap Parameters on the Aerodynamic Performance of a Wind-Turbine Airfoil

A numerical method has been used to analyze the flow field related to a NACA 0015 airfoil with and without a flap and assess the influence of the flap height and angle on the surface pressure coefficient,lift coefficient,and drag coefficient.The numerical results demonstrate that the flap can effectively improve the lift coefficient of the airfoil;however,at small attack angles,its influence is significantly reduced.When the angle of attack exceeds the critical stall angle and the flap height is 1.5%of the chord length,the influence of the flap becomes very evident.As the flap height increases,the starting point of the separation vortex gradually moves forward and generates a larger wake vortex.Optimal aerodynamic characteristics are obtained for 1.5%(of the chord length)flap height and a 45°flap angle;in this case,the separation vortex is effectively reduced.

Investigation of water impingement on a multi-element high-lift airfoil by Lagrangian and Eulerian approach

McDonnell Douglas Aerospace(MDA)high-lift model is widely used in the study of multi-element airfoil,while there is still short knowledge of ice accretion and water impingement on it.In this paper,based on two-phase flow theory,two numerical models were presented by using both Eulerian approach and Lagrangian approach,respectively,in order to predict the water impingement efficiency on a two-dimensional(2D)multi-element high-lift airfoil.Both computational results were validated with the experiment data,which shown good agreements in the impingement limitations and tendency.The trend that how the attack angle and droplet diameter affect the feather of local water impingement characteristics on the different elements of MDA were further investigated.As shown in this research,the trends that the local impingement intensity and extent on flap of MDA varied differently as in general understanding due to the complex structures of flow field,which should be careful cognized in design of the ice protection system.

A STUDY ON THE MECHANISM OF HIGH-LIFT GENERATION BY AN AIRFOIL IN UNSTEADY MOTION AT LOW REYNOLDS NUMBER

The aerodynamic force and flow structure of NACA 0012 airfoil performing an unsteady motion at low Reynolds number (Re = 100) are calculated by solving Navier-Stokes equations. The motion consists of three parts: the first translation, rotation and the second translation in the direction opposite to the first. The rotation and the second translation in this motion are expected to represent the rotation and translation of the wing-section of a hovering insect. The flow structure is used in combination with the theory of vorticity dynamics to explain the generation of unsteady aerodynamic force in the motion. During the rotation, due to the creation of strong vortices in short time, large aerodynamic force is produced and the force is almost normal to the airfoil chord. During the second translation, large lift coefficient can be maintained for certain time period and (C) over bar (L), the lift coefficient averaged over four chord lengths of travel, is larger than 2 (the corresponding steady-state lift coefficient is only 0.9). The large lift coefficient is due to two effects. The first is the delayed shedding of the stall vortex. The second is that the vortices created during the airfoil rotation and in the near wake left by previous translation form a short 'vortex street' in front of the airfoil and the 'vortex street' induces a 'wind'; against this 'wind' the airfoil translates, increasing its relative speed. The above results provide insights to the understanding of the mechanism of high-lift generation by a hovering insect.

Optimization design study of low-Reynolds-number high-lift airfoils for the high-efficiency propeller of low-dynamic vehicles in stratosphere

Aerodynamic performance of low-Reynolds-number high-lift airfoil makes a great impact on designing a high-efficiency propeller for low-dynamic vehicles in stratosphere. At high altitude,low-Reynolds-number airfoils are supposed to have high lift-drag ratio or high endurance factor at cruising attack angle along with good stall characteristics. To design such a high-performance low-Reynolds-number high-lift airfoil,the paper established a hierarchical multi-objective optimization platform by combing direct search optimization algorithm EXTREM and airfoil flow field solver XFOIL to automatically and quickly calculate aerodynamic performance function of airfoil by computer. It provides an effective solution to multi-point design problem of low-speed low-Reynolds-number airfoil. It can be seen from the results of three typical optimization examples,the new airfoil E387_OPT2,FX63-137_OPT2 and S1223_OPT2 based on hot low-Reynolds-number high-lift airfoils (Eppler 387 airfoil,Wortmann FX63-137 airfoil and S1223 airfoil) can meet the optimization design requirements and have very good aerodynamic characteristics in both design state and non-design state. Thus,the applicability and effectiveness of hierarchical multi-objective optimization platform are verified.

Low-Speed Aerodynamic Characteristics of Supercritical Airfoil with Small High-Lift Devices from Flow Pattern Measurements

In this paper, the lift coefficients of SC-0414 airfoil are estimated by applying modified Yamana’s method to the flow visualization results, which are obtained by utilizing the smoke tunnel. The application of the modified Yamana’s method is evaluated with two calculation methods. Additionally, the lift estimation, wake measurements, and numerical simulations are performed to clarify the low-speed aerodynamic characteristics of the SC airfoil with flaps. The angle of attack was varied from −5° to 8°. The flow velocity was 12 m/s and the Reynolds number was 1.6 × 105. As a result, the estimated lift coefficients show a good agreement with the results from reference data and numerical simulations. In clean condition, the lift coefficients calculated from the two methods show quantitative agreement, and no significant difference could be confirmed. However, the slope of the lifts calculated from ys is higher and closer to the reference data than those obtained from sc, where ys denotes the height where the distance from the streamline to the reference line is the largest, and sc denotes the displacement of the center of pressure from the origin of the coordinate, respectively. In the case of flaps, the GFs have an observable effect on the aerodynamic performance of the SC-0414 airfoil. When the height of the flap was increased, the lift and drag coefficients increased. The installation of a GF with a height equal to 1% of the chord length of the airfoil significantly improved the low-speed aerodynamic performance of SC airfoils.

Numerical Study on Low-Reynolds Compressible Flows around Mars Helicopter Rotor Blade Airfoil

High-speed rotor rotation under the low-density condition creates a special low-Reynolds compressible flow around the rotor blade airfoil where the compressibility effect on the laminar separated shear layer occurs. However, the compressibility effect and shock wave generation associated with the increase in the Mach number (M) and the trend change due to their interference have not been clarified. The purpose is to clear the compressibility effect and its impact of shock wave generation on the flow field and aerodynamics. Therefore, we perform a two-dimensional unsteady calculation by Computational fluid dynamics (CFD) analysis using the CLF5605 airfoil used in the Mars helicopter Ingenuity, which succeeded in its first flight on Mars. The calculation conditions are set to the Reynolds number (Re) at 75% rotor span in hovering (Re = 15,400), and the Mach number was varied from incompressible (M = 0.2) to transonic (M = 1.2). The compressible fluid dynamics solver FaSTAR developed by the Japan aerospace exploration agency (JAXA) is used, and calculations are performed under multiple conditions in which the Mach number and angle of attack (α) are swept. The results show that a flow field is similar to that in the Earth’s atmosphere above M = 1.0, such as bow shock at the leading edge, whereas multiple λ-type shock waves are observed over the separated shear layer above α = 3° at M = 0.80. However, no significant difference is found in the Cp distribution around the airfoil between M = 0.6 and M = 0.8. From the results, it is found that multiple λ-type shock waves have no significant effect on the airfoil surface pressure distribution, the separated shear layer effect is dominant in the surface pressure change and aerodynamic characteristics.

Fourier neural operator with boundary conditions for efficient prediction of steady airfoil flows

An efficient data-driven approach for predicting steady airfoil flows is proposed based on the Fourier neural operator(FNO),which is a new framework of neural networks.Theoretical reasons and experimental results are provided to support the necessity and effectiveness of the improvements made to the FNO,which involve using an additional branch neural operator to approximate the contribution of boundary conditions to steady solutions.The proposed approach runs several orders of magnitude faster than the traditional numerical methods.The predictions for flows around airfoils and ellipses demonstrate the superior accuracy and impressive speed of this novel approach.Furthermore,the property of zero-shot super-resolution enables the proposed approach to overcome the limitations of predicting airfoil flows with Cartesian grids,thereby improving the accuracy in the near-wall region.There is no doubt that the unprecedented speed and accuracy in forecasting steady airfoil flows have massive benefits for airfoil design and optimization.

Design and Structure Optimization of Plenum Chamber with Airfoil Baffle to Improve Its Outlet Velocity Uniformity in Heat Setting Machines

The plenum chamber of a heat setting machine is a key structure for distributing hot air to different air channels.Its outlet velocity uniformity directly determines the heating uniformity of textiles,significantly affecting the heat setting performance.In a traditional heat setting machine,the outlet airflow maldistribution of the plenum chamber still exists.In this study,a novel plenum chamber with an airfoil baffle was established to improve the uniformity of the velocity distribution at the outlet in a heat setting machine.The structural influence of the plenum chamber on the velocity distribution was investigated using a computational fluid dynamics program.It was found that a chamber with a smaller outlet partition thickness had a better outlet velocity uniformity.The structural optimization of the plenum chamber was conducted using the particle swarm optimization algorithm.The outlet partition thickness,the transverse distance and the longitudinal distance of the optimized plenum chamber were 20,686.2 and 274.6 mm,respectively.Experiments were carried out.The experimental and simulated results showed that the optimized plenum chamber with an airfoil baffle could improve the outlet velocity uniformity.The air outlet velocity uniformity index of the optimized plenum chamber with an airfoil baffle was 4.75%higher than that of the plenum chamber without an airfoil baffle and 5.98%higher than that of the conventional chamber with a square baffle in a commercial heat setting machine.

Optimized Design of H-Type Vertical Axis Wind Airfoil at Multiple Angles of Attack

Numerical simulations are conducted to improve the energy acquisition efficiency of H-type vertical axis wind turbines through the optimization of the related blade airfoil aerodynamic performance.The Bézier curve is initi-ally used tofit the curve profile of a NACA2412 airfoil,and the moving asymptote algorithm is then exploited to optimize the design of the considered H-type vertical-axis wind-turbine blade airfoil for a certain attack angle.The results show that the maximum lift coefficient of the optimized airfoil is 8.33%higher than that of the original airfoil.The maximum lift-to-drag ratio of the optimized airfoil exceeds the maximum lift-to-drag ratio of the ori-ginal airfoil by 11.22%.Moreover,the power coefficient is increased by 12.19%and the torque coefficient of the wind turbine is significantly improved.

改变导叶翼型对水泵水轮机“S”特性的影响

针对水泵水轮机“S”特性区域的不稳定性问题,提出使用改型活动导叶翼型进行性能提升.以某水泵水轮机模型为研究对象,采用SST k-ω湍流模型对水泵水轮机全流道进行三维数值计算,通过对活动导叶翼型的改型设计,得出流量-转速模拟曲线,分析水泵水轮机组“S”特性改善情况.将计算与试验结果进行对比,并对改型活动导叶翼型前后机组的无叶区进行压力脉动分析.结果表明:在保证整体效率依然保持在92%附近的前提下,新的活动导叶翼型对机组的“S”特性依旧具有改善效果;无叶区压力脉动主要是受到活动导叶叶栅区域的分流在此重新聚集影响,并且与转轮叶片的动静相互扰动引起的;改型后的活动导叶降低了无叶区的压力脉动幅值,提升了水泵水轮机运行中的并网稳定性.

复杂地形对风速廓线的影响

随着风电利用的发展,越来越多的风电场建立在复杂地形的山区,为了更好地进行风能评估和风电预报,就需要了解复杂地形对风速廓线的影响。本文基于薄翼理论和湍流边界层扰动的线性化理论,采用两层模型对坡度较小的山地在其二维横截面上的风廓线进行了预测,该模型能够较为准确地预报地形、压力、稳定度对风速增速的影响,但对于三维地形或其他因素产生的风速的复杂变化,需要进一步将其扩展至三维,并结合数值模拟进行研究。

翼型叶片安装方式对粉煤灰气力输送的影响

针对当前螺旋流气力输送中有关叶片安装方式的研究,分析了典型NACA系列翼型截面叶片应用于起旋装置时的流场。通过对观测面轴向流速与切向流速的仿真,计算叶片不同安装方式与安装角度时螺旋流场的旋流强度,确定了前缘迎风的安装方式比尾缘迎风起旋效果更强;安装方式固定时,旋流强度随安装角度的增大而减小。

风电NACA63418翼型参数化建模及优化

风力发电机的风轮气动效率与优良翼型的气动性能密切相关。以风力机传统翼型为研究对象,结合翼型参数化建模及自适应遗传算法,寻优搜索得到高性能优化翼型。比较了CST法和改进的Hicks-Henne型函数法对于NACA63418传统翼型的拟合精度,进而选用Hicks-Henne型函数法对NACA63418翼型进行参数化建模。通过自适应遗传算法和XFOIL软件耦合实现翼型气动特性的自动计算,提高翼形的设计效率,为翼型的理论设计拓宽了思路。

前缘圆柱对风力机翼型气动性能及冲蚀磨损影响研究

为研究风沙环境下流动控制方式对于NACA 0012翼型气动性能和冲蚀磨损的影响,通过在风力机翼型前缘布置微小圆柱来控制气流流动,采用离散项模型和SST k-ω湍流模型对控制翼型进行数值计算。结果表明:攻角较小时,微小圆柱处于X=0.04、Y=-0.03位置时控制效果最佳,可抑制流动分离,相比原翼型升阻比提高149.72%;微小圆柱处于X=0.02、Y=-0.02位置时翼型冲蚀磨损的减小量最大,相比原翼型减小97.66%;微小圆柱处于最优区域时翼型升阻比提高的同时冲蚀磨损量也会减小。

多参数变弯度翼型气动优化设计方法

为了获得机翼最优的气动外形,提出了一种多偏转参数与非均匀B样条结合的翼型前后缘连续偏转变形方法。以NACA3412翼型为研究实例,对翼型曲线进行参数化重构。以翼型前、后缘偏转位置和偏转角度为变化参数,模拟分析了不同变形状态对翼型气动特性的影响规律。以翼型升力系数和升阻比为优化目标,以前、后缘的偏转角度、偏转位置以及过渡段长度等六个偏转参数为设计变量,采用多目标遗传算法和ANSYS软件进行优化设计。结果表明,与基础翼型相比,优化后的变弯度翼型的升阻比提升约19.26%,升力提升约44.43%,明显改善了翼型的气动性能。

非对称升力翼对高速列车横风气动性能的影响

随着高速列车运行速度的不断提升,横风环境下列车运行安全问题日益凸显。为此,从控制气动升力角度提出一种非对称升力翼结构以期形成抗倾覆力矩,并采用数值模拟方法,对比分析原始车型、全展开升力翼车型和收缩迎风侧升力翼车型的气动载荷及列车周围流场结构,探究横风环境下该结构对列车横风气动性能的影响。研究结果表明:升力翼对高速列车气动载荷及周围流场影响显著;列车安装升力翼后主要改变了车顶和车体背风侧表面压力分布以及车顶、车体背风侧和尾流区域的速度分布;车体顶部由于受到非对称升力翼压力面影响,在升力翼下方车顶区域形成了低速高压区且向车体背风侧延伸;同时,车体背风侧表面压力升高,在升力翼下游车体背风侧空间区域,由流动分离导致的漩涡结构发生了明显改变;相比于原始车型,收缩迎风侧升力翼车型(模型Ⅱ和模型Ⅲ)均可减小列车横向力和倾覆力矩;模型Ⅲ效果最显著,3车编组列车横向力和倾覆力矩分别减少13.19%和11.86%。

S型翼缝与尾缘襟翼联合控制风力机翼型气动性能的研究

降低叶片气动载荷对于延长风力机叶片寿命极为重要,尾缘襟翼是降低叶片气动载荷的一种有效手段,然而其在大攻角下对翼型的气动特性控制效果减弱。通过在50%叶片弦长处添加S型翼缝,采用数值模拟方法研究S型翼缝与尾缘襟翼联合调节风力机叶片气动特性的作用。利用剪切应力输运(shear stress transport,SST)湍流模型,计算模拟了S809翼型在雷诺数106下,S型翼缝与尾缘襟翼联合控制对翼型气动特性的影响,并分析了S型翼缝与尾缘襟翼的协同控制机理。结果表明,尾缘襟翼的偏转可显著改变翼缝槽内的气体流量,并有效调节叶片中部的压差,这种联合控制策略可在大攻角下大幅改善翼型的失速现象,从而显著增强尾缘襟翼对升力系数的调控能力。

气动升力协同列车升力翼优化设计研究

气动升力协同列车是一种新型高速列车的概念模型,旨在提高运行速度的同时兼顾列车整体耗能与寿命周期成本。其通过加装升力翼,提高列车的气动升力,从而减少列车轮毂磨损。为设计出适合现有高铁限界约束的升力翼,本文采用Hicks-Henne翼型参数化方法和遗传算法,建立了考虑列车外型与高铁限界约束的气动优化方法,并利用此方法开展了翼型优化设计,以优化翼型为基础设计了加装翼梢小翼的三维升力翼模型。研究表明:采用本文优化设计方法得到的优化翼型,相比基础翼型,升力系数提升13%,阻力系数几乎不变。加装翼梢小翼可以有效的减小升力翼的气动阻力,通过对比不同外倾角和后掠角的小翼气动特性,设计出了一种外倾角为15°、后掠角为30°的较优升力翼模型,其最大升力系数可达到1.8247。