鸭式旋翼/机翼飞机悬停及小速度前飞气动干扰实验研究

鸭式旋翼/机翼飞机是一种新概念可垂直起降高速飞行器,为了解该飞机在悬停及小速度前飞时的全机气动干扰特性,在南京航空航天大学开口风洞中进行了飞机全机气动力实验,实验采用多台测力天平分别测量主机翼和机身的气动力.结果表明,悬停时受主机翼高速旋转产生的下洗尾流影响,机身产生了较大的法向力和低头力矩;前飞时下洗尾流对机身的法向力和俯仰力矩有比较严重的干扰,对滚转力矩和偏航力矩干扰较小,对侧向力有一定影响.实验结果为飞机的飞行动力学特性研究以及控制律设计提供了参考.＃     

旋翼尾流与地面干扰时地面涡现象的研究

用Ｎ－Ｓ方程对近地飞行时旋翼尾流与地面干扰时产生的地面涡现象进行了数值计算旋翼对流场的作用由分布在特定区域内的动量源项模拟结果表明，旋翼尾流撞到地面后的卷起和轴向流动的拉伸作用是形成地面涡的原因；地面边界层形成的二次分离涡向地面涡内输入（与尾流所携带的涡量）相反的涡量，而使地面涡保持平衡；地面涡的存在和运动使旋翼附近流场大大改变     

A comprehensive PIV measurement campaign on a fully equipped helicopter model

The flow field around a helicopter is characterised by its inherent complexity including effects of fluid?Cstructure interference, shock?Cboundary layer interaction, and dynamic stall. Since the advancement of computational fluid dynamics and computing capabilities has led to an increasing demand for experimental validation data, a comprehensive wind tunnel test campaign of a fully equipped and motorised generic medium transport helicopter was conducted in the framework of the GOAHEAD project. Different model configurations (with or without main/tail rotor blades) and several flight conditions were investigated. In this paper, the results of the three-component velocity field measurements around the model are surveyed. The effect of the interaction between the main rotor wake and the fuselage for cruise/tail shake flight conditions was analysed based on the flow characteristics downstream from the rotor hub and the rear fuselage hatch. The results indicated a sensible increment of the intensity of the vortex shedding from the lower part of the fuselage and a strong interaction between the blade vortex filaments and the wakes shed by the rotor hub and by the engine exhaust areas. The pitch-up phenomenon was addressed, detecting the blade tip vortices impacting on the horizontal tail plane. For high-speed forward flight, the shock wave formation on the advancing blade was detected, measuring the location on the blade chord and the intensity. Furthermore, dynamic stall on the retreating main rotor blade in high-speed forward flight was observed at r/R?=?0.5 and 0.6. The analysis of the substructures forming the dynamic stall vortex revealed an unexpected spatial concentration suggesting a rotational stabilisation of large-scale structures on the blade.     

Effect of a moving wall on a fully developed, equilibrium turbulent boundary layer

Experiments were conducted in a wind tunnel to assess the effect of a moving wall on a fully developed, equilibrium turbulent boundary layer. Pitot-static and total head probes were used in conjunction with both single- and two-component hot-wire anemometer probes to quantify the effect of wall motion on the boundary layer velocity statistics. A variable speed, seamless belt formed the wind tunnel test section wall. When stationary, the belt was found to possess a fully developed, equilibrium turbulent boundary layer in excellent agreement with archival data. With the tunnel wall moving at the free-stream speed, and at a sufficient distance above the wall, the velocity statistics in the moving-wall boundary layer were found to collapse well when scaled as a self-preserving turbulent wake. The near-wall mean velocity profile of the moving wall was found to exhibit an extended region of linearity compared to canonical turbulent boundary layer and internal flows. This can be attributed to the reduced shear resulting from wall motion and the subsequent reduction in Reynolds stress. Received: 2 June 1999/Accepted: 8 August 2000     

一种风力机气动计算的全自由涡尾迹模型

采用全自由方式建立风力机尾流场的涡尾迹模型,引入“虚拟周期”的概念,并发展一种自适应松弛因子方法,从而改善了自由尾迹迭代的稳定性,提高了迭代收敛速度。利用建立的自由涡尾迹模型,计算了风力机叶片的尾流场结构、气动性能及叶片载荷,并与实验结果进行了对比分析。结果表明,尖速比越大,自适应松弛因子方法对缩小模型计算时间越有效;全自由涡尾迹模型能准确给出风力机尾流场的结构,包括尾迹的扩张以及叶尖涡和叶根涡的产生、发展和耗散的过程,风轮扭矩与实验数据吻合;叶片载荷分布的计算结果在低风速下与实验值基本一致,但是在大风速下差别较大,说明需要一个准确的失速模型。     

A nonlinear model for aerodynamic configuration of wake behind horizontal-axis wind turbine

Determination of the aerodynamic configuration of wake is the key to analysis and evaluation of the rotor aerodynamic characteristics of a horizontal-axis wind turbine.According to the aerodynamic configuration, the real magnitude and direction of the onflow velocity at the rotor blade can be determined, and subsequently, the aerodynamic force on the rotor can be determined. The commonly employed wake aerodynamic models are of the cylindrical form instead of the actual expanding one. This is because the influence of the radial component of the induced velocity on the wake configuration is neglected. Therefore, this model should be called a "linear model". Using this model means that the induced velocities at the rotor blades and aerodynamic loads on them would be inexact. An approximately accurate approach is proposed in this paper to determine the so-called "nonlinear" wake aerodynamic configuration by means of the potential theory,where the influence of all three coordinate components of the induced velocity on wake aerodynamic configuration is taken into account to obtain a kind of expanding wake that approximately looks like an actual one. First, the rotor aerodynamic model composed of axial(central), bound, and trailing vortexes is established with the help of the finite aspect wing theory. Then, the Biot-Savart formula for the potential flow theory is used to derive a set of integral equations to evaluate the three components of the induced velocity at any point within the wake. The numerical solution to the integral equations is found,and the loci of all elementary trailing vortex filaments behind the rotor are determined thereafter. Finally, to formulate an actual wind turbine rotor, using the nonlinear wake model, the induced velocity everywhere in the wake, especially that at the rotor blade,is obtained in the case of various tip speed ratios and compared with the wake boundary in a neutral atmospheric boundary layer. Hereby, some useful and referential conclusions are offered for the aerodynamic computation and design of the rotor of the horizontal-axis wind turbine.     

Methods for investigating supersonic ground effect in a blowdown wind tunnel

Two methods to experimentally investigate supersonic ground effect problems in a wind tunnel have been examined to determine their relative effectiveness compared to a more realistic, but physically unfeasible, representation of the ground effect by means of a moving ground. Experimental data were compared with the results of numerical simulations. The latter, once validated against pressure data from the wind tunnel, confirmed that generally a symmetry technique is more suitable than an elevated ground approach.     

用鲁棒Riemann求解器和运动重叠网格计算旋翼粘性绕流

发展了一种基于鲁棒Riemann求解器和运动重叠网格技术计算直升机悬停旋翼流场的方法。基于惯性坐标系,悬停旋翼流场是非定常流场,控制方程为可压缩Reynolds平均Navier-Stoke方程,其对流项采用Roe近似Reimann求解器离散,使用改进的五阶加权基本无振荡格式进行高阶重构,非定常时间推进采用含牛顿型LUSGS子迭代的全隐式双时间步方法。为实施旋转运动和便于捕捉尾迹,计算采用运动重叠网格技术。计算得到的桨叶表面压力分布及桨尖涡涡核位置都与实验结果吻合较好。数值结果表明:所发展方法对桨尖涡具有较高的分辨率,对激波具有较好的捕捉能力,该方法可进一步推广到前飞旋翼粘性绕流的计算。     

Time-resolved wake structure and kinematics of bat flight

We present synchronized time-resolved measurements of the wing kinematics and wake velocities for a medium sized bat, Cynopterus brachyotis, flying at low-medium speed in a closed-return wind tunnel. Measurements of the motion of the body and wing joints, as well as the resultant wake velocities in the Trefftz plane are recorded at 200 Hz (approximately 28–31 measurements per wing beat). Circulation profiles are found to be quite repeatable although variations in the flight profile are visible in the wake vortex structures. The circulation has almost constant strength over the middle half of the wing beat (defined according the vertical motion of the wrist, beginning with the downstroke). A strong streamwise vortex is observed to be shed from the wingtip, growing in strength during the downstroke, and persisting during much of the upstroke. At relatively low flight speeds (4.3 m/s), a closed vortex structure behind the bat is postulated.     

Assessment of a high‐order MUSCL method for rotor flows

This work presents the implementation of a high‐order, finite‐volume scheme suitable for rotor flows. The formulation is based on the variable extrapolation MUSCL‐scheme, where high‐order spatial accuracy (up to fourth‐order) is achieved using correction terms obtained through successive differentiation. A variety of results are presented, including 2‐ and 3‐dimensional test cases. Results with the proposed scheme, showed better wake and higher resolution of vortical structures compared with the standard MUSCL, even when coarse meshes were employed. The method was also demonstrated for 3‐dimensional unsteady flows using overset and moving grids for the UH‐60A rotor in forward flight and the Enhanced Rotorcraft Innovative Concept Achievement tiltrotor in aeroplane mode. For medium grids, the present method adds reasonable CPU and memory overheads and offers good accuracy on relatively coarse grids.     

扰动风作用下微型旋翼流场的数值模拟及流动控制研究

对于处在低雷诺数下的微型旋翼,扰动风对其流场影响很大。本文基于动态嵌套网格技术的双时间法,采用网格速度法模拟扰动风,研究了不同频率和幅值的正弦式扰动风下三维微型旋翼上的拉力系数响应情况,并采用变形网格方法模拟了旋翼桨叶的周期性边距运动对扰动风的流动控制,为今后旋翼机的主动控制研究提供了线索。研究结果表明,低雷诺数下,旋翼在周期性扰动风作用下的拉力响应曲线拟合函数与扰动风函数形式相同,响应曲线函数同样具有周期性变化趋势,波动幅值与扰动风幅值成正比例关系;对不同飞行状态下的旋翼,采用周期等角变距方式,能够找到一个适合的控制参数使得旋翼在正弦式扰动风环境下旋翼的拉力波动在一定范围内得到有效抑制。     

Quantitative studies of the wakes of freely flying birds in a low-turbulence wind tunnel

A novel application of DPIV methods is presented for measuring velocity and vorticity distributions in vertical cross sections through the wake of a freely flying bird (thrush nightingale) in a wind tunnel. A dual-camera system is used, and successive cross-correlation operations remove lens/camera distortions, and then the undisturbed background flow, so that the final operation simply examines the disturbance effect of the bird alone. The concentration and tuning of processing methods to the disturbance quantities allows full exploitation of the correlation calculation and estimation algorithms. Since the ultimate objective is to deduce forces and power requirements on the bird itself from the wake structure, the analytical procedure is followed through an example on a fixed airfoil, before sample results from extensive bird flight tests are described. The wake structure of the thrush nightingale in slow (5-m/s) flight is qualitatively quite similar to those previously described in the literature, but certain quantitative details are different in important respects.An erratum to this article can be found at     

Optical vortex tracking studies of a horizontal axis wind turbine in yaw using laser-sheet, flow visualisation

 Experimental studies have been conducted on a 0.9 m diameter, horizontal axis wind turbine (HAWT) placed in the open jet of a closed return wind tunnel. The turbine was tested in a three blade and a two blade configuration. The power coefficient of the turbine was measured and wake flow studies conducted for a range of yawed flows by tilting the rotor plane at various angles up to 30° to the incident wind direction. The motion of the shed vorticity was followed using laser-sheet flow visualisation with the overall wake deflection being measured. The results were compared with theoretical predictions and with studies conducted elsewhere. Received: 24 October 1996 / Accepted: 16 May 1997     

风剪切对风力机叶片气动性能及尾迹形状的影响

风力机通常运行在非定常工况中,其气动性能及尾迹会随着工况的变化而变化.风剪切是风力机长期所处的环境,它会影响到叶片气动载荷、尾迹形状、总体性能等,分析风剪切作用下的叶片气动性能对风力机的设计有重要意义.本文采用一种时间步进自由涡尾迹(free vortex wake,FVW)方法,耦合FVW方法与风剪切模型,计算不同风...     

An unsteady multiblock multigrid scheme for lifting forward flight rotor simulation

Numerical simulation of multi‐bladed lifting rotors in forward flight is considered. The flow‐solver presented is multiblock and unsteady, which is essential for forward flight, and also includes multigrid acceleration to reduce run‐times. A structured multiblock grid generator specifically for rotor blades has also been developed and is presented here. Previous work has shown that hovering lifting rotor flows are particularly expensive to simulate, since the capture of the vortical wake below the disc requires a long numerical integration time; more than 20 revolutions for an unsteady simulation, or more than 40000 time‐steps for a single grid steady simulation. It is demonstrated here that only two or three revolutions are required to obtain a converged solution for forward flight, since the wake is swept downstream. This requires less than 1.5 × the run‐time of a steady hovering simulation, for the same grid density around each blade, even though an unsteady simulation is required and the complete disk must be solved rather than one blade as in hover. It is demonstrated that very fine meshes are required to capture the unsteady tip vortex motion, and the effects on blade loading of blade‐vortex interaction and rotor shaft inclination are also considered. Copyright © 2004 John Wiley & Sons, Ltd.     

两种椭圆翼型高速气动特性实验研究

新概念旋转机翼飞机的主机翼既能高速旋转作为旋翼,又可锁定作为固定翼,所以只能使用特殊的前后对称翼型。针对主机翼翼型的这一特殊要求,对16％相对厚度,相对弯度分别为0％和3％的两种椭圆翼型的高速气动特性进行了风洞实验研究,试验分别在中国空气动力研究发展中心FL-21风洞和荷兰代尔夫特大学TST-27风洞进行,采用表面测压和尾排型阻测量技术。试验结果的对比分析表明,有弯度椭圆翼型的升力和力矩特性优于无弯度椭圆翼型,而阻力特性和最大升阻比劣于无弯度椭圆翼型。试验结果为旋转机翼飞机主机翼翼型的选取提供了参考。     

高超声速飞行器气动热关联换算方法研究

气动热风洞实验是地面研究和预测飞行器气动热环境的重要手段之一, 但由于风洞实验模拟能力的限制, 风洞实验的流场参数和模型的几何尺度都会与实际飞行情况存在一定的差别, 导致地面风洞实验中得到的模型表面气动加热率数据无法直接用于飞行条件下的热环境预测和热防护设计. 以往通过针对具体飞行器的试验结果进行数据拟合后外插的气动热关联换算方法指向性较强, 没有考虑到气动热的具体影响参数, 存在一定局限性, 难以外推应用于其他外形的飞行器. 为解决通过气动热风洞实验数据外推预测飞行条件下气动热的技术难题, 基于无量纲NS方程和边界层理论分析研究了影响气动热的主要参数, 并通过推导化简边界层近似解热流公式, 针对层流流态建立了气动热关联换算方法, 可以考虑当地边界层外缘参数的影响, 具有一定通用性. 在此基础上, 利用建立的方法将Reentry-F飞行器缩比模型的风洞实验数据换算到该飞行器飞行条件下的典型工况, 并与飞行测量结果进行了比较, 外推预测结果与飞行测量结果符合较好, 表明建立的关联方法可以用于气动热风洞实验数据的外推换算.      

Determination of real-time predictors of the wind turbine wake meandering

The present work proposes an experimental methodology to characterize the unsteady properties of a wind turbine wake, called meandering, and particularly its ability to follow the large-scale motions induced by large turbulent eddies contained in the approach flow. The measurements were made in an atmospheric boundary layer wind tunnel. The wind turbine model is based on the actuator disc concept. One part of the work has been dedicated to the development of a methodology for horizontal wake tracking by mean of a transverse hot wire rake, whose dynamic response is adequate for spectral analysis. Spectral coherence analysis shows that the horizontal position of the wake correlates well with the upstream transverse velocity, especially for wavelength larger than three times the diameter of the disc but less so for smaller scales. Therefore, it is concluded that the wake is actually a rather passive tracer of the large surrounding turbulent structures. The influence of the rotor size and downstream distance on the wake meandering is studied. The fluctuations of the lateral force and the yawing torque affecting the wind turbine model are also measured and correlated with the wake meandering. Two approach flow configurations are then tested: an undisturbed incoming flow (modelled atmospheric boundary layer) and a disturbed incoming flow, with a wind turbine model located upstream. Results showed that the meandering process is amplified by the presence of the upstream wake. It is shown that the coherence between the lateral force fluctuations and the horizontal wake position is significant up to length scales larger than twice the wind turbine model diameter. This leads to the conclusion that the lateral force is a better candidate than the upstream transverse velocity to predict in real time the meandering process, for either undisturbed (wake free) or disturbed incoming atmospheric flows.     

How far the wake of a wind farm can persist for?

With the increased penetration of wind energy in our nation’s energy portfolio, wind farms are placed in a way close to each other. Thus, their wakes have to be fully considered in the design and operation of a wind farm. In this study, we investigate the wake of a wind farm using large-eddy simulation with wind turbine rotor modelled by the actuator disk model. The simulated results show that the wake of a wind farm can persist for a long distance in its downstream. For the considered wind farm layout, the velocity in the wake recovers 95% of that of the undisturbed inflow at 55 rotor diameters downstream from its last row, suggesting that the wake of a wind farm should be fully considered in the optimal design and operation for its downstream wind farms.