直流式低速风力试验平台的设计改进

搭建设计直流式风力试验平台,使用皮托管在试验段不同位置及不同深处进行风流的速度,压力及温度测试,并采用蜂窝器和整流网对平台的流场品质进行改进,对于风流的均匀性及稳定性进行测试及比较,结果表明,改进后的直流式试验平台具有良好的风流流场,具备开展小模型的吹风试验的基本条件。

果园风送喷雾风力调控试验台设计及试验

目前,果园风送喷雾技术与装备正在朝着精准化和智能化方向发展。果园喷雾控制对象主要为喷施药量和风力供给量,果树冠层内外药液沉积分布很大程度上取决于风送系统风力供给,只有风力和药量均得到精确控制,才能实现果园对靶精准喷雾。为此,基于轴流风机设计了风机转速、进风口面积和出风口导流板倾斜角度可独立调控的果园风送喷雾风力调控试验台,通过直流电机调速实现风机转速调节;进风口采用百叶结构,通过调节百叶倾斜角度实现进风口开度大小调节;出风口采用塔式结构,通过22路舵机控制出风口不同喷头位置处导流板倾斜角度独立调节,并基于C#语言开发了上位机界面。利用试验平台开展了风机转速、进风口面积和出风口导流板倾斜角度独立调控风力变化特性试验,结果表明:出风口风速风量变化与风机转速和进风口面积调节呈正相关,出风口风速在垂直方向分布位置随导流板倾斜角度增加发生改变,同时分别建立了出风口最大风速与风机转速和进风口面积之间的关系模型。喷药过程中,可通过风机转速与导流板倾斜角度联合调节或进风口面积与导流板倾斜角度联合调节实现出风口风速风量在果树冠层垂直方向分布位置和大小调节。研究结果为实现根据果树冠层体积和枝叶稠密度变化进行风力在线调控提供了一种新方法,对加快果园精准喷雾技术应用具有重要意义。

旋桨式堤防漏洞险情探测仪的应用试验分析

基于动水头压力和流速差原理,研究了一种旋桨式手持堤防漏洞险情探测仪,分别通过开展风力试验、水力试验等多次试验检测验证该设备实际效果。试验研究表明,该装置能在堤防迎水坡快速精准探测堤防漏洞入水口位置,在试验条件各工况下,该探测仪具有一定的可行性。同时,在室内、堤防现场试验情况下对该仪器进行应用分析,可为类似堤防抢险工作提供参考。

国外航空气动技术在风力机上的应用进展

风力机气动技术是提高风能捕获能力的核心技术。在调研近两年国外文献资料的基础上,概述了航空气动技术在风力机上应用的最新研究进展。主要包括水平轴大型风力机发展的新概念、垂直轴风力机专用翼型研究、各种气动技术在叶片上的应用研究、美国缩尺风场技术设备(SWi FT)建设和测试技术发展。目的是跟踪国外风力机气动布局概念和技术应用研究进展,意在为我国该领域研究工作提供参考。

LED路灯照明应用之探讨

本文根据LED路灯的使用特点,在配光曲线对LED路灯的均匀度影响方面做了分析,提出了几种平均照度的计算方法和人们容易忽视的环境比SR值和LED路灯特有的安全问题。也结合LED的优点提出了智能控制技术的应用,最后是对LED路灯美观方面的一些期望。

Relevance of zero lift drag coefficient and lift coefficient to Mach number for large aspect ratio winged rigid body

Synthetic analysis is conducted to the wind tunnel experiment results of zero lift drag coefficient and lift coefficient for large aspect ratio winged rigid body.By means of wind tunnel experiment data,the dynamics model of the zero lift drag coefficient and lift coefficient for the large aspect ratio winged rigid body is amended.The research indicates that the change trends of zero lift drag coefficient and lift coefficient to Mach number are similar.The calculation result and wind tunnel experiment data all verify the validity of the amended dynamics model by which to estimate the zero lift drag coefficient and lift coefficient for the large aspect ratio winged rigid body,and thus providing some technical reference to aerodynamics character analysis of the same types of winged rigid body.

风电机组并网脉冲宽度调制整流器的算法

采用合适的脉冲宽度调制(PWM)整流器算法解决风电机组并网产生冲击的问题被广泛关注,研究了采用直流电压反馈控制和滞环电流控制相结合的算法实现的三相平衡可逆式PWM整流器,可实现风电机组输出功率的稳定。介绍了该算法中各单元的数学模型,以及已用于风力发电试验台进行仿真和实测的情况。实测结果验证了该算法的正确性。

Wind tunnel testing of wind pressures on a large gymnasium roof

A wind tunnel test was conducted for a large steel gymnasium structure. Simultaneous pressure measurements were made on its entire ellipsoidal roof in a simulated suburban boundary layer flow field. Special attention is paid to the charaeteristics of fluctuating wind pressures in different zones on the roof. Some selected results are presented： 1） correlations between fluctuating wind pressures on both roof surfaces, 2） eigenvalues and eigenvectors of covariance matrices of the fluctuating wind pressures, 3） probability distributions of the fluctuating wind pressures, and 4） statistical characteristics of peak factor. Furthermore, the applicability of the quasi-steady approach is discussed in detail. Based on the results, an empirical formula for estimating the minimum pressure coefficients, using a peak factor approach, is presented. Comparison of the minimum pressure coefficients determined by the proposed formula and those obtained from the wind tunnel tests is made to examine the applicability and accuracy of the proposed formula.

Wind tunnel tests on aerodynamic characteristics of vehicles on same-storey highway and rail bridge under crosswind

In recent years,the safety and comfort of road vehicles driving on bridges under crosswinds have attracted more attention due to frequent occurrences of wind-induced disasters.This study focuses on a container truck and CRH2 high-speed train as research targets.Wind tunnel experiments are performed to investigate shielding effects of trains on aerodynamic characteristics of trucks.The results show that aerodynamic interference between trains and trucks varies with positions of trains(upstream,downstream)and trucks(upwind,downwind)and numbers of trains.To summarize,whether the train is upstream or downstream of tracks has basically no effect on aerodynamic forces,other than moments,of a truck driving on windward sides of bridges(upwind).In contrast,the presence of trains on the bridge deck has a significant impact on aerodynamic characteristics of a truck driving on leeward sides(downwind)at the same time.The best shielding effect on lateral forces of trucks occurs when the train is located downstream of tracks.Finally,the pressure measuring system shows that only lift forces on trains are affected by trucks,while other forces and moments are primarily affected by adjacent trains.

Validation of DFIG and PMSG Wind Turbines' LVRT Capabilities Through Real Field Tests

Low voltage ride through (LVRT) capability has become more and more an issue for newly integrated wind turbines. The LVRT programs described in this paper developed field tests for newly installed wind turbines on wind farms in Northeast China. It is therefore different from other papers that only validate LVRT control strategies through running computer software simulations. To examine a single wind turbine's LVRT capability, the wind turbine's terminal voltage dip was realized by using a grid voltage dip emulator, which was located on the 690 V side of the generator transformer. In this paper, by artificially making various grid faults, the dynamic behavior of DFIG and PMSG wind turbines are analyzed and compared, control strategies such as active/passive crowbar and chopper protection schemes are verified, and new active/reactive power compensation methods are investigated and compared.

NUMERICAL MODELING STUDY OF EFFECTS OF EASTERN PACIFIC WARM POOL ON ENSO

In this study, sensitivity experiments were conducted with the Zebiak-Cane ocean-atmosphere coupled model forced by the wind stress anomaly from the U.S. National Centers for Environmental Prediction/National Center for Atmospheric Research （NCEP/NCAR） reanalysis data to study the impacts of eastern Pacific warm pool on the formation and development of ENSO events. The effects of climatological mean sea surface temperature of the warm pool on forecast skill during the ENSO events of 1982-1999 are more considerable that those of climatological mean meridional winds and ocean currents. The forecast skill for the 1997/1998 E1 Nifio event is characterized by sensitivity to climatological mean sea surface temperature and anomalies of northerly winds and currents. The forecast skill is found insensitive to climatological mean northerly meridional winds and currents.

Conceptual Design and Aerodynamic Study of Joined-Wing Business Jet Aircraft

The concept of joined-wing aircraft with nonplanar wings as conceived and patented by Wolkovitch is attractive due to various advantages such as light weight, high stiffness, low induced drag, high trimmed CLmax, reduced wetted area and parasite drag and good stability and control, which have been supported by independent analyses, design studies and wind tunnel tests. With such foreseen advantages, the present work is carried out to design joined-wing business-jet aircraft and study and investigate its advantages and benefits as compared to the current available conventional business jet of similar size, passenger and payload capacity. In particular, the work searches for a conceptual design of joined-wing configured business-jet aircraft that possesses more superior characteristics and better aerodynamic performance in terms of increased lift and reduced drag, and lighter than the conventional business jet of similar size. Another significant objective of this work is to prove that the added rigidity possessed by the joined wing configuration can contribute to weight reduction.

Test Rig Effect on Performance Measurement for Low Loaded Large-Diameter Fan for Automotive Application

Large diameter fans with low solidity are widely used in automotive application for engine cooling. Their designs with small chord length help reducing the torque on the electrical motor and providing a good aerodynamic compromise between several operating conditions, some of these being at high flow rate. Their global performances are measured according to the ISO standard DP 5801, which allows comparison of results from different facilities. However, some variations in global performances are observed when considering results from two different test rigs. On a fan selected for the purpose of this study, up to 6 % of efficiency is lost on the worst case. As efficiency is more than ever a key factor to select a component, some experimental and numerical investigations were conducted to analyze the fan behavior on each facility. Two sets of measurement and simulation are performed and compared. Geometries considered for the domain of computation include the test rig plenum, the torquemeter, the ground and a large domain for the atmospheric conditions. The exact fan geometry with tip clearance and under-hub ribs is also considered. Numerical results show a good agreement with experiment in both cases when convergence is reached and for low flow rate when computations are switched to unsteady mode. Comparisons show that simulations are able to capture the different fan behaviors depending on the confguration and those efficiency losses previously observed are correctly predicted. These results are further analyzed to perform some post-processing. Blade loading remains identical for both cases but disparities appear in the wake and its interaction with the surrounding. Tiny details that are often neglected during experiment and/or simulation appear to be the cause of slight variations. Position of the torquemeter and shape of the plenum are among the parameters that various and that have cumulative effects. Efficiency being a ration of pressure and torque, variations are rather important. Finally, these results are discussed in terms of rules for conception and a new geometry less sensible to loss of efficiency is proposed.

Experimental Investigation of Reynolds Number Effect on Wind Turbine Profiles in the Cryogenic Wind Tunnel Cologne DNW-KKK

Wind turbine size has increased continuously and correspondingly also its Reynolds numbers. The Reynolds number effect can therefore no longer be ignored in design and optimization of wind turbines. Reliable profile test data should be available. A suitable facility for testing wind turbine profiles at high Reynolds numbers is the Cryogenic Wind Tunnel Cologne DNW-KKK. By means of injecting liquid nitrogen the tunnel can be cooled down to 100 K and the Reynolds number therefore can be raised accordingly. The maximum Reynolds number for 2D profile tests can reach 27x10^6. In this paper the test uncertainty and the flow quality of DNW-KKK were analyzed. Then some test results on the Reynolds number effect of the wind turbine profiles will be presented. The Reynolds number effect is different from model to model. Especially for thick profiles and flow control devices the Reynolds number effect is not always like the description in literature.

A Ducted Fan MAV Anti-torque Control System

The UAVs （unmanned aerial vehicles） exist in various sizes. One of the most interesting niches concerns the UAVs of moderate size （〈 1 m）, also called MAVs （micro air vehicles）. An aerodynamic study of the ULB （Universite Libre de Bruxelles） developed a ducted rotor MAV using the results of full-scale wind tunnel tests that allowed the determination of the platform speed envelope, the power requirements and the endurance characteristics for ISA sea level conditions. Although the ULB MAV appears similar to other ducted-rotor concepts, it fundamentally differs from them as it uses the downwash of a single rotor to compensate the electric motor main rotor torque and to achieve full control around the roll, pitch and yaw axes. This paper explains in detail the components layout of the MAV and the aerodynamic characteristics of the anti-torque blades.

Introducing CFD and Wind Tunnel Testing in an Undergraduate Fluid Mechanics Course

CFD （computational fluid dynamics） is following the trend of CAD and FEA （finite element analysis） to undergraduate education especially with recent advances in commercial codes. It will soon take its place as an expected skill for new engineering graduates. CFD was added as a component to an experiment in a junior level fluid mechanics course. The objectives were to introduce CFD, as an analysis tool, to the students and to support the theoretical concepts of the course. The students were asked to complete an experimental two-dimensional study for a wing in a wind tunnel, to use CFD to simulate the flow, and to predict the aerodynamic lift using CFD as well as the experimentally obtained pressure distribution. In addition, they had to compare their results to published data for the studied wing. Details of the course, the wind tunnel test and the CFD simulations are presented. Samples from the students＇ work are used in the discussion. The lab activities were successfully completed by the students and the learning objectives were well addressed. One of the valuable outcomes from this lab was the opportunity for the students to integrate multiple fluid mechanics analysis tools and learn about the limits for each tool. CFD also enhanced the learning in the lab activities and increased students＇ interest in the subject.

风力发电技术现状及展望

1 引言风能是一种没有污染、洁净的可再生能源。风能在自然界中取之不尽,用之不竭,潜力巨大。据气象组织统计,全世界风能资源约为200亿 kW,约为可利用水力资源的10倍。我国风能资源约16亿 kW。

Static aeroelastic analysis of a high-aspect-ratio wing based on wind-tunnel experimental aerodynamic forces

The aeroelastic responses of a high-aspect-ratio wing are investigated based on nonlinear experimental aerodynamic forces. The influences of nonlinear experimental aerodynamic forces and dynamic pressures on the wing loads are studied in the longitudinal and lateral maneuver states. The flight loads of the wing fixed at the root are calculated at different angles of attack. The aileron efficiency with respect to the dynamic pressures and aileron deflections are also studied. The results indicate that the flight loads of the wings vary nonlinearly with the angle of attack and dynamic pressure. Due to the high-lift aerofoil, elastic components are a large portion of the wing loads, especially for small angles of attack and high dynamic pressure condi-tions. The aileron efficiency is significantly affected by aileron deflections, dynamic pressures and angles of attack when the nonlinear experimental aerodynamic forces are used for calculation. In states with high dynamic pressures and large aileron deflections, aileron reversal can occur. The aileron deflection and angle of attack have a nonlinear effect on the aileron efficiency. An efficient method for analyzing the flight loads and structural design of high-aspect-ratio wings is derived in this study, and the analysis can provide insight into the distribution of flight loads for high-aspect-ratio wings.

Numerical Study of Effects of Mach number on Aerodynamic Performance of Large Enthalpy Drop Stationary Cascade

Based on the method to change blade loading type along blade height, that is, applying aft-loading at both end zones of cascade while applying fore-loading in the mid zone of cascade, HTC(Harbin Turbine Company) designed a twisted and bowed stationary cascade with low aspect ratio and large enthalpy drop. To verify the aerodynamic performance of such cascade, firstly, low-speed wind tunnel tests were conducted to validate the calculation results of commercial software CFX, and then numerical simulations were made for the aerodynamic performance of the cascade at different Mach numbers. The simulation results show that the large enthalpy drop stationary cascade designed by HTC can offer good aerodynamic performance while keeping its high-load characteristics in the change range of outlet Mach number as stated in this paper.