Influence of blade-tower interaction in upwind-type horizontal axis wind turbines on aerodynamics

The blade-tower interaction of upwind horizontal axis wind turbines has become important to aerodynamic loading as the systems become larger. However, there are not enough studies describing these phenomena. To investigate this interaction, we performed numerical simulations for uniform, yawed, wind shear flow conditions, and various tower cases using the nonlinear vortex correction method with time-marching free wake. At 5 m/s, the change in the normal force coefficient is approximately 10% of the average. The blade root region has a larger azimuth range of the interaction and a bigger change in aerodynamic loading. The blade-tower interaction decreases as the yaw error and wind shear exponent increases. The interaction due to tower radius variations is higher than that due to tower clearance variations. With regard to stochastic load, the blade-tower interaction may affect the total fatigue load at low wind speed and in a more unstable atmospheric condition.     

折叠变体飞行器风洞试验模型研发

变体飞行器一直是航空领域研究的热点问题.针对某变体飞行器风洞试验任务提出的运动性能指标,设计开发了可控的折叠变体试验模型,对其设计方案及工作原理进行了阐述,对折叠变体机构进行了运动学与动力学分析,建立了位移、速度和加速度控制的数学模型,得出了机构的最大受力状态及各连接杆件的最大受力值,并进行了角度误差的分析与计算.结果表明,该试验模型能够对机翼折叠变体角度进行连续、稳定和精确控制,完全达到了设计要求的各项指标.     

Effect of body angle on the aerodynamics of a rhinoceros beetle: Smoke-wire visualization in a wind tunnel

In the present study, flow structure around a live rhinoceros beetle in a tethered flight is investigated experimentally using a smoke-wire visualization technique in a wind tunnel with a free-stream velocity of 1.2 m/s, which is close to that of a typical flight speed. While varying the body angle (from 5 to 85°), the flow structures generated by the hindwings, elytra, and body are visualized along the spanwise direction. During the flapping period, the complex flow structures comprised leading-edge, trailing-edge, and tip vortices generated on the hindwing, but the flow structure is quite simple on the elytra (attached flow) and body (separated flow). As the body angle increases, these vortices convect in the downward direction, which matches the observation that the body angle of a hovering flight is larger than that of a forward flight. When the body angle matches the condition of forward flight, it is also found that the Strouhal number of a flapping hindwing is tuned to 0.4, which is known as an optimal value for thrust efficiency. Further, the effect of free-stream velocity (i.e., advance ratio) on the formation and evolution of these coherent vortical structures are investigated.

     

Investigation on aerodynamics and active flow control of a vertical axis wind turbine with flapped airfoil

A 2D unsteady numerical simulation with dynamic and sliding meshing techniques was conducted to solve the flow around a threeblade Vertical axis wind turbine (VAWT). The circular wakes, strip-like wakes and the shedding vortex structures interact with each other result in an extremely unstable performance. An airfoil with a trailing edge flap, based on the NACA0012 airfoil, has been designed for VAWT to improve flow field around the turbine. Strategy of flap control is applied to regulate the flap angle. The results show that the flapped airfoil has an positive effect on damping trailing edge wake separation, deferring dynamic stall and reducing the oscillating amplitude. The circular wake vortices change into strip vortices during the pitch-up interval of the airfoils. Examination of the flow details around the rotating airfoil indicates that flap control improves the dynamic stall by diminishing the trend of flow separation. Airfoil stall separation has been suppressed since the range of nominal angle of attack is narrowed down by an oscillating flap. Vortices with large intensity over rotational region are reduced by 90 %. The lift coefficient hysteresis loop of flapped airfoil acts as an O type, which represents a more stable unsteady performance. With flap control, the peak of power coefficient has increased by 10 % relative to the full blade VAWT. Obviously, the proposed flapped airfoil design combined with the active flow control significantly has shown the potential to eliminate dynamic stall and improve the aerodynamic performance and operation stability of VAWT.     

Experimental and numerical studies of wingtip and downwash effects on horizontal tail

Journal of Mechanical Science and Technology - Studying wing downwash, which is caused by the wingtip effect, and its influence on horizontal tail is important for aircraft design. In this work,...     

机场地面风和大风的特征分析及其对飞行的影响

利用气象常规资料,对昆明机场近几年来的地面平均风速以及大风进行分析,找到容易影响飞行安全的大风出现的月份、时段以及引起大风的主要天气现象和大风出现时的天气状况,并总结其特点,为以后可能出现的影响飞行安全的大风和风切变的预测提供参考依据。     

A parametric study on the influence of boundary conditions on the longitudinal pressure gradient in CFD simulations of an automotive wind tunnel

Computational fluid dynamics (CFD) is an important and extensively used tool for aerodynamic development in the vehicle industry today. Validation of virtual methods by comparison to wind tunnel experiments is a must because manufacturers aim to substitute physical tests on prototype vehicles with virtual simulations. An appropriate validation can be performed only if the wind tunnel geometry with representative boundary conditions is included in the numerical simulation, and if the flow of the empty wind tunnel is accurately predicted. One of the important flow parameters to predict is the longitudinal pressure distribution in the test section, which is dependent on both the wind tunnel geometry and the settings of the boundary layer control systems. This study investigates the effects of flow angularity at the inlet and different boundary layer control systems, namely, basic scoop suction, distributed suction, and moving belts, on the longitudinal pressure distribution in the full-scale aerodynamic wind tunnel of Volvo Cars using CFD and a systematic design of experiments approach. The study shows that the different suction systems used to reduce boundary layer thickness upstream of the vehicle have statistically significant effects on the longitudinal pressure distribution in the test section. However, the estimated drag difference induced on a typical vehicle by the difference in horizontal buoyancy between the tested settings is within the test-to-test uncertainty of the physical wind tunnel, thereby leading to the conclusion that force calculations in simulations are fairly insensitive to the tested parameters on the investigated intervals.

     

地铁隧道壁面冲洗装置的结构研究

地铁隧道施工完成后会在隧道壁堆积大量污泥灰尘,为了能实现隧道壁的自动清洗,设计出一种隧道壁面冲洗结构。根据隧道的形状,将冲洗结构分成三个模块,每个模块能独立控制。同时,冲洗结构的姿态由液压系统控制,水压系统提供水源,使整个装置具有响应快,运动平稳的特点。     

Numerical studies on two turbulence models and a laminar model for aerodynamics of a vertical-axis wind turbine

The purpose of this study is the analysis of flow around a one-bladed Darrieus-type wind turbine using computational fluid dynamics (CFD). The rotor geometry consists of a NACA 0015 airfoil with chord length of 0.15 m. Numerical simulations are performed using ANSYS Fluent, employing laminar model and two turbulence models: SST k-ω and RNG k-ε. The obtained numerical results of unsteady aerodynamic blade loads are compared with available experimental results from literature. Computed aerodynamic characteristics of normal and tangential forces comply with the experiment results. The RNG k-ε turbulence model has a good accuracy in determining aerodynamic blade loads for the upwind and downwind parts of the rotor. The laminar model and the SST k-ω turbulence model slightly overestimate the tangential aerodynamic blade loads at the downwind part of the rotor. An averaged wind turbine velocity profile computed at one rotor radius downstream of the rotor has a Gaussian shape. The steady-state airfoil characteristics are computed for the Reynolds number comparable to the Reynolds number of a moving blade employing the SST k-ω and RNG k-ε turbulence models and using the same computational grid as for unsteady simulations of the rotor.     

外掠横风下槽式聚光器应力与变形特性研究

以槽式太阳能聚光器为研究对象,设计了一种新型结构的槽式太阳能支架.利用ANSYSWorkbench软件对聚光器进行流固耦合数值模拟,得到聚光器在正常工作最大风速6级风作用下不同工况下变形、等效应力和拉应力安全系数等数据,结果表明:新型支架在各工况下变形都很小;拉应力安全系数远远大于零;新型聚光器的工作角度为30°时是最差工况;风向与主光轴的夹角越大,镜面上的压力分布越向离风近的一侧集中.     

电火花线切割中热效应现象及其对模具质量影响

热效应是电火花线切割加工模具时的固有现象,将热效应影响范围分为7个区,并分析对模具质量的影响,指出模具热效应区中的过热区和淬火区产生的残余应力和微裂纹是影响模具制造质量的重要原因,并制定相应的解决办法与对策.实例表明,用热效应现象分析和解决模具电火花线切割的质量问题是非常有效的.     

双向清洗系统研究及其在爬壁机器人上的应用

针对建筑物玻璃幕墙的清洗要求和目前机器人只能单向清洗作业的实际情况,开发了一种与爬壁机器人配套使用、具备双向作业及污水回收净化循环利用功能的清洗作业系统,大幅提高了作业质量、作业效率和节能环保性能.清洗系统不但适用于已有的爬壁机器人,也可与具有较强吸附运动功能及壁面适应能力、但在垂直于壁面方向有一个移动自由度的轮腿式爬壁机器人配套使用.开发了用于清洗系统与机器人集成的高度自适应弹性连接机构,实现了清洗系统恒压越障、恒压作业功能,且作业范围进一步扩大至弧形壁面,最后给出了该清洗系统与连接机构在轮腿式爬壁机器人上的应用示例.     

卧式数控机床主轴温度场分布及对机床热变形的影响

分别应用红外热像仪测温技术和激光测距技术对机床温度场和机床热误差开展研究.着重分析三轴卧式数控机床的温度场分布、机床运行中的热行为以及两者之间的联系.经试验发现,主轴热误差是数控机床的主要误差源之一,主轴热误差与机床运行中的温度分布有紧密联系,主轴各方向变形量呈现出随主轴温度升高而明显增大趋势,并且主轴Z方向的伸长量远大于X和Y向的变形量.提出通过改善冷却和散热条件而降低主轴温度,以达到有效控制主轴热误差以及建立热变形补偿模型实施补偿等措施,经验证热变形改善效果明显.     

隧道钢拱架安装车小臂水平减振研究

为了减轻小臂水平欠阻尼振动对钢拱架对接操作的影响,研究了基于电磁式换向阀阀芯位置调整的小臂减振控制系统。系统根据小臂实时转角角度和角速度,输出控制信号调节阀芯位置,使小臂在换向阀开启过程具有更平滑的速度变化和完全关闭后更小的角速度遗留量;通过建立AMESim-Simulink联合仿真模型,对比研究了传统PID控制器和模糊PID控制器在小臂减振控制系统上的应用效果。仿真及实验结果显示,控制系统使得单次响应时间被控制在10s内,稳态误差控制在1%以下,有效地减轻了振动的影响,缩短了连续操作的时间间隔,且模糊控制的响应速度和控制精度更高。     

超音速风洞大口径蝶阀流场分析及改进

介绍了超音速风洞大口径蝶阀的配置形式。运用COSMOSFloWorks软件分析了不同结构蝶板及蝶阀不同开度情况下的流场情况。通过在蝶板上增加蒙皮以及在蒙皮上开孔的方式改善了蝶阀的流场,蝶阀配置旁路阀的方式改善了蝶阀的使用工况,从而降低了蝶阀的故障率,延长了蝶阀的使用寿命。     

On the impact of anemometer size on the velocity field in a closed wind tunnel

In the present paper, experimental and numerical investigations of the flow around different types and sizes of anemometers are presented and discussed.The measurements of the flow field at different distances upstream of the anemometer are performed with a laser Doppler Anemometer. The computational results are in good agreement with the experimental ones since the observed deviations are of the same order of magnitude. These results show that anemometers may induce a strong distortion of the velocity field, even far upstream of the anemometer. This distortion has to be taken into account in the anemometer calibration field to yield reliable and consistent measurements.     

基于热电偶的低速风洞气流温度误差补偿方法

低速风洞气流温度数据质量是影响风洞流场品质的关键,针对热电偶测量导热误差和辐射误差补偿方法开展了专项研究。具体基于传热学基本原理,开展了基于热电偶丝浸入长度定值导热误差补偿方法、周围温度相对变化率定值辐射误差补偿方法研究,得到了热电偶浸入长度和周围温度相对变化率与温度测试误差之间定量关系的仿真结果。为了对于误差机理分析和仿真结果进行验证,开展了风洞验证试验。试验结果表明：热电偶浸入误差实测结果与理论仿真结果基本一致,周围温度相对变化率ω<1,可以降低温度测量辐射误差对于温度均匀性影响7.12倍。所提方法对于气体介质条件下热电偶工程应用提供了有益探索和技术依据。     

基于虚拟设计制造技术的大型风洞设备开发

FL-9低速增压风洞是"十五"国家批准建设的大型航空基础设施,以其开发研制为背景,运用制造业信息化技术,构建了大型风洞设备的虚拟设计制造平台.此平台具备网络系统支持下的设备三维数字化设计、计算机辅助分析、计算机辅助工艺设计、可视化及三维交互等功能.并建立了风洞设备设计制造信息化体系,实现了设计制造全过程信息分类代码的规范和统一.基于此平台开发的FL-9低速增压风洞经5年的研制已全面建成并首次试车成功.     

基于UG和ADAMS的砂尘风洞转台系统的虚拟设计

以沙尘风洞转台系统的开发研制为背景,提出了一种基于UG和ADMS的机械系统虚拟设计流程,介绍了UG和ADAMS在砂尘风洞试件试验位置调整用的单轴转台系统中的应用,并详细阐述了UG和ADAMS的图形数据交换方法.所提出的设计方法成功地解决风洞转台的设计与匹配问题,有效地缩短了设计周期.