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.

Study on Aerodynamic Performance of Wind Turbine Airfoil Synthesized by Mean Camber Line Superposition Thickness between Bionic and Traditional Airfoil Bionic and Traditional Airfoil

The aerodynamic performance of wind turbine needs to be improved day by day.In this paper,the bionic airfoil of wind turbine and the traditional airfoil are combined to optimize the aerodynamic performance.The new airfoil is synthesized by the method of the mean camber line superposition thickness synthesis.The flow field characteristics of 4 synthetic airfoils were calculated by using the numerical simulation of CFD commercial software Fluent,and compared with 3 original airfoils,new airfoils of different shapes were obtained,and an incomplete synthetic parameterization method for airfoils optimization was proved,which has certain engineering practical value.

Research on Leading Edge Erosion and Aerodynamic Characteristics of Wind Turbine Blade Airfoil

The effects of the erosion present on the leading edge of a wind turbine airfoil(DU 96-W-180)on its aerodynamic performances have been investigated numerically in the framework of a SST k–ωturbulence model based on the Reynolds Averaged Navier-Stokes equations(RANS).The results indicate that when sand-induced holes and small pits are involved as leading edge wear features,they have a minimal influence on the lift and drag coefficients of the airfoil.However,if delamination occurs in the same airfoil region,it significantly impacts the lift and resistance characteristics of the airfoil.Specifically,as the angle of attack grows,there is a significant decrease in the lift coefficient accompanied by a sharp increase in the drag coefficient.As wear intensifies,these effects gradually increase.Moreover,the leading edge wear can exacerbate flow separation near the trailing edge suction surface of the airfoil and cause forward displacement of the separation point.

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.

小尺寸切开式尾缘锯齿对翼型气动噪声的影响

研究小尺寸切开式尾缘锯齿对翼型气动噪声的影响,并分析齿高与尾缘边界层厚度之间的关系对降噪效果的影响.以NACA0012翼型为研究对象,采用混合计算气动声学方法进行仿真.在20 m/s风速下对NACA0012翼型进行噪声实验,验证仿真方法的准确性.通过控制齿高和齿宽研究不同形状尾缘锯齿分别在0°和10°攻角下对翼型气动噪声的影响.研究结果表明,尾缘锯齿的降噪效果与齿高和齿宽均成正比.0°攻角下最大降噪量为3.3 dB,10°攻角下最大降噪量为2.6 dB.切开式尾缘锯齿结构会增加流向噪声的高频分量,尤其在0°攻角下显著.相比嵌入式尾缘锯齿,切开式尾缘锯齿具有更小的极限降噪齿高.

固定转捩对不同系列及厚度翼型气动性能的影响研究

为探究翼型表面污染对其气动性能的影响,基于SST k-ω模型对DU、NACA44XX系列的不同厚度翼型的气动性能进行数值模拟,确定两系列翼型的固定转捩敏感位置,分析固定转捩对两系列及不同厚度翼型气动参数、失速特性及内流特征的影响。结果表明:不同的气动外形会明显改变翼型的转捩敏感位置,但相对厚度的变化不会对其产生影响,DU和NACA44XX系列翼型吸力面和压力面上的转捩敏感位置分别位于1%c、5%c处及1%c、9%c处;NACA44XX翼型受固定转捩的影响相较于DU翼型更大,并随厚度的增大其影响更加显著;相对厚度增大导致固定转捩位置附近的高涡量区和整体涡团尺寸进一步增大,气动外形和相对厚度对固定转捩敏感度的影响主要体现在尾缘处的分离涡。

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。

基于遗传算法的磁悬浮列车升力翼的翼型及外形结构优化

翼型对于高速列车升力翼的气动性能影响明显,为进一步提高升力翼的增升性能,对磁悬浮列车升力翼的翼型和外形结构优化很有必要。选用翼型NACA BR 63-55-12作为高速列车升力翼的基础翼型,利用遗传算法与CFD相结合的方法对基础翼型进行优化,对基础翼型和优化后的翼型进行气动性能对比分析,在此基础上建立了升力翼的气动仿真模型,研究了翼尖小翼和支撑杆形状对气动性能的影响。结果表明:优化后翼型气动特性出现明显提升,其中升力系数提高23.2%,阻力系数降低0.67%,升阻比提高;升力翼翼尖加装小翼起到增强翼尖涡耗散作用,安装小翼的升力翼的升阻比平均增大约6.7%;升力翼的3种截面中椭圆形的支撑杆阻力最小,在3种截面形状中最大。

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。

中/低雷诺数翼型后缘纯音噪声物理机制与主/被动控制研究综述

基于国内外研究成果,本文总结了中/低雷诺数下翼型后缘纯音噪声的物理机制与主/被动控制的研究现状,阐述了目前该研究还需回答与解决的部分问题,并对可能的新研究思路与方法进行了展望。在物理机制方面,边界层内声反馈和后缘涡脱落是公认的中/低雷诺数下翼型后缘纯音噪声的2种主要发声机制。前者由T–S不稳定波散射噪声向上游传播、在边界层与翼型后缘之间形成,产生的纯音噪声具有典型“阶梯状”离散频谱特性;后者由翼型尾流整体不稳定性引起,纯音噪声具有单一频率特性。2种发声机制之间如何竞争以及噪声频率如何选择等问题仍未完全解决。在研究方法方面,主要采用线性稳定性分析、风洞实验测量和DNS/LES数值模拟等研究方法。由于现有研究的翼型较为单一,所得结果无法满足翼型低噪声设计的需求。在噪声控制方面,被动控制方法多采用翼型前/后缘锯齿、多孔材料和柔性壁面,主动控制方法多采用表面吹/吸气和等离子体技术;在基于机理分析有效抑制翼型后缘纯音噪声方面,还有较多可改进之处。

翼型结构对印刷电路板换热器流动与换热特性影响

印刷电路板换热器(PCHE)作为超临界二氧化碳(S-CO_(2))布雷顿循环中的重要设备,其性能会影响系统的效率。为了提高翼型PCHE性能,探究翼型翅片结构对其流动与换热性能的影响。本工作针对S-CO_(2)布雷顿循环系统中的高温回热器,采用数值模拟的方法,选用S-CO_(2)为传热工质。通过对3种不同结构的NACA0020的翼型翅片通道的流动与换热性能进行比较,研究翼型翅片最大厚度在弦长上的位置参数对换热器的性能影响,并从热工水力性能、综合性指标、整体流动性、局部性能等方面分析了变化规律。结果表明,在翼型翅片结构中保持相对厚度不变的情况下,随着翼型翅片最大厚度在弦长上越接近翼型前缘的位置,其换热性能也会随之提高。其中NACA0020-20的翼型翅片通道在选定的工况条件下,j因子和Nu比其他两种翼型翅片通道大2.7%~8.8%和2.7%~8%,并且该翼型翅片结构可以有效地减小边界层所带来的影响,提高了其PCHE的换热性能,其综合性能更是优于其他两种翼型翅片。研究结果对于翼型PCHE的结构设计和性能优化提供了一定的依据。

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。