大风区铁路沿线挡风墙积沙机理及优化措施的风洞实验研究

位于兰州至新疆的兰新二线是世界上首条穿越大风区的高速铁路,途径著名的烟墩风区、百里风区、三十里风区及达坂城风区,风区段铁路里程长达 462.4 km,占新疆段线路总长的 65.1${\%}$,大风对铁路的运营、养护和运输造成很大危害. 为了降低大风对通行列车的危害,兰新铁路沿线设置了大量挡风墙. 挡风墙发挥作用的同时,也带来了铁路沿线的积沙问题. 为了解决这一工程实践的现实问题,本文提出了在现有挡风墙背风侧的不同位置处,设立第二道挡墙以减弱铁路积沙的治理思路,并开展了对应条件下对现有单道挡风墙、以及在现有单道挡风墙背风侧坡顶处和坡脚处设置第二道挡墙,共计3种情景的风洞模拟实验,发现设置第二道挡墙后距轨道线路高0.1 m处的沙粒水平速度、数密度、输沙通量及沉积率较无第二道挡墙时明显减少,介于8%$\sim$12${\%}$,51%$\sim$69${\%}$,20%$\sim$73${\%}$以及26%$\sim $38${\%}$,而且在现有单道挡风墙背风侧坡顶部增设第二道挡风墙的效果更好. 因此,本文的研究成果有助于优化大风区已有铁路沿线、城镇等防沙治沙工程措施.      

轮背空腔-密封气对CAES向心涡轮变工况流动损失的影响

本文以国内首套MW级压缩空气储能(CAES)系统末级向心涡轮为研究对象,通过数值模拟分析了变工况条件下轮背空腔-密封气对等熵效率和流场结构的影响.结果表明:在求解中考虑轮背空腔-密封气结构能够使等熵效率数值解的偏差减小0.7%;随涡轮进口压力增加,轮背空腔泄漏流由叶片吸力面中部叶高区域逐渐向轮毂转移,流动损失先增加后减小;合理降低轮背空腔泄漏气体的轴向速度,能够减弱轮背空腔-密封气结构对等熵效率的负面影响,使向心涡轮在较宽的变工况范围内都保持高效运行.     

The stability analysis of rolling motion of hypersonic vehicles and its validations

The stability of the rolling motion of near space hypersonic vehicles with rudder control is studied using method of qualitative analysis of nonlinear differential equations, and the stability criteria of the deflected rolling motions are improved. The outcomes can serve as the basis for further study regarding the influence of pitching and lateral motion on the stability of rolling motion. To validate the theoretical results, numerical simulations were done for the rolling motion of two hypersonic vehicles with typical configurations. Also, wind tunnel experiments for four aircraft models with typical configurations have been done. The results show that: 1) there exist two dynamic patterns of the rolling motion under statically stable condition. The first one is point attractor, for which the motion of aircraft returns to the original state. The second is periodic attractor, for which the aircraft rolls periodically. 2) Under statically unstable condition, there exist three dynamic patterns of rolling motion, namely, the point attractor, periodic attractor around deflected state of rolling motion, and double periodic attractors or chaotic attractors.     

新型双通道Mach-Zehnder干涉仪多普勒测风激光雷达鉴频系统研究及仿真

Mach-Zehnder(M-Z)干涉仪可作为鉴频器件应用于多普勒测风激光雷达系统中.鉴于一般M-Z干涉仪的稳定性差,不易于调节的缺点,提出一种基于双棱镜结构的新型双通道M-Z干涉仪作为多普勒测风激光雷达鉴频器件.在进行探测原理分析的基础上,利用光学设计软件对其鉴频系统结构进行了参量优化设计和系统仿真.通过设定实验参量并进行光线追迹模拟仿真实验结果,应用反演理论获得了风速值.利用多普勒频移公式计算获得理论风速并与仿真结果进行了对比,结果表明反演仿真风速与理论风速值基本吻合,标准差为0.46m/s.此新型双通道M-Z干涉仪可以作为鉴频器件应用于多普勒测风激光雷达系统中,在光路的调节及提高系统稳定性上具有优势.     

Wind turbine fault detection using multiwavelet denoising with the data-driven block threshold

Rapid expansion of wind turbines has drawn attention to reduce the operation and maintenance costs. Continuous condition monitoring of wind turbines allows for early detection of the generator faults, facilitating a proactive response, minimizing downtime and maximizing productivity. However, the weak features of incipient faults in wind turbines are always immersed in noises of the equipment and the environment. Wavelet denoising is a useful tool for incipient fault detection and its effect mainly depends on the feature separation and the noise elimination. Multiwavelets have two or more multiscaling functions and multiwavelet functions. They possess the properties of orthogonality, symmetry, compact support and high vanishing moments simultaneously. The data-driven block threshold selected the optimal block length and threshold at different decomposition levels by using the minimum Stein’s unbiased risk estimate. A multiwavelet denoising technique with the data-driven block threshold was proposed in this paper. The simulation experiment and the feature detection of a rolling bearing with a slight inner race defect indicated that the proposed method successfully detected the weak features of incipient faults.     

不同交通流状态下桥梁气动导数的风洞试验研究

为了考虑实际运营车辆对桥梁气动导数的影响,根据车辆密度模拟了三种交通流状态,基于强迫振动装置,分别对每个交通流和无车状态下的桥梁气动导数进行风洞试验研究,讨论了不同攻角下不同车流的车辆对桥梁气动导数的影响,探究了车辆对气动导数影响的百分比以及气动导数变化量的变化规律。研究结果表明:不同攻角下不同车流的车辆均对直接导数A*2、H*4和交叉导数A*4、H*2影响显著,A*2、A*3变化量随着折减风速有一定的变化规律。虽然不同攻角下不同车流的车辆对气动导数的影响程度及影响规律不同,并且车流的繁忙程度对大多数气动导数的影响规律不明显,但是车辆对桥梁气动导数的影响不容忽略。     

横摆角下汽车尾部湍流特征量的PIV试验分析

汽车尾部湍流场是汽车压差阻力的主要来源,在HD-2汽车模型风洞中,首先使用测力天平和测压系统,对横摆角工况下汽车模型的气动六分力和纵对称截面48个测点的表面压力进行了测量,然后利用PIV测量技术对模型在横摆角分别为0°、15°的尾部湍流场进行了测量,获得该模型尾流场的速度场、涡量场和雷诺应力流场信息,通过计算得出尾流场区域空间相关系数和湍流积分尺度。结果表明:在横摆角工况下,汽车模型尾部涡流的结构呈现向上发展的趋势;尾流场拖拽涡的范围和强度的增大导致了模型气动力出现较大的增加;湍流积分尺度的变化表明,尾部涡流区的分离噪声与涡流分离位置有关,在汽车尾部造型设计中,要尽量推迟尾部涡流的分离。     

Study on the operational safety of high-speed trains exposed to stochastic winds

The characteristic wind curve （CWC） was com- monly used in the previous work to evaluate the operational safety of the high-speed trains exposed to crosswinds. How- ever, the CWC only provide the dividing line between safety state and failure state of high-speed trains, which can not evaluate the risk of derailment of high-speed trains when ex- posed to natural winds. In the present paper, a more realistic approach taking into account the stochastic characteristics of natural winds is proposed, which can give a reasonable and effective assessment of the operational safety of high-speed trains under stochastic winds. In this approach, the longitudi- nal and lateral components of stochastic winds are simulated based on the Cooper theory and harmonic superposition. An algorithm is set up for calculating the unsteady aerody- namic forces （moments） of the high-speed trains exposed to stochastic winds. A multi-body dynamic model of the rail vehicle is established to compute the vehicle system dynamic response subjected to the unsteady aerodynamic forces （mo- ments） input. Then the statistical method is used to get the mean characteristic wind curve （MCWC） and spread range of the high-speed trains exposed to stochastic winds. It is found that the CWC provided by the previous analyticalmethod produces over-conservative limits. The methodol- ogy proposed in the present paper can provide more signif- icant reference for the safety operation of high-speed trains exposed to stochastic winds.     

Transient simulation of a pump-turbine with misaligned guide vanes during turbine model start-up

Experimental studies of a model pump-turbine S-curve characteristics and its improvement by misaligned guide vanes （MGV） were extended to prototype pump turbine through 3-D transient flow simulations. The unsteady Reynolds-averaged Navier-Stokes equations with the SST turbulence model were used to model the transient flow within the entire flow passage of a reversible pump-turbine with and without misaligned guide vanes during turbine model start-up. The unstable S-curve and its improvement by using misaligned guide vane were verified by model test and simulation. The transient flow calculations were used to clarify the variations of pressure pulse and internal flow behavior in the entire flow passage. The use of misaligned guide vanes can eliminate the S-curve characteristics of a pump-turbine, and can significantly increase the pressure pulse amplitude in the entire flow passage and the runner radial forces during start-up. The MGV only decreased the pulse amplitude on the guide vane suction side when the rotating speed was less than 50% rated speed. The hydraulic reason is that the MGV dramatically changed the flow patterns inside the entire flow passage, and destroyed the symmetry of the flow distribution inside the guide vane and runner.     

Aeroelastic analysis of wind turbines using a tightly coupled CFD–CSD method

This paper presents aeroelastic analyses of wind turbines, using the compressible flow Helicopter Multi-Block (HMB2) solver of Liverpool University, coupled with a Computational Structural Dynamics method. For this study, the MEXICO and NREL Phase VI wind turbines were employed. A static aeroelastic method was first employed for the analysis of the MEXICO blade and the effect of the torsional stiffness was studied at 10, 15 and 24 m/s axial wind speeds. The torsional deformations showed strong dependency on this parameter and the blade region from mid-span to the tip was the most susceptible to aeroelastic effects. The work progressed by studying both the static and dynamic response on the NREL wind turbine, where the nacelle and the tower were considered. Mean deflections between the static and dynamic methods showed consistency and, due to the structural properties of this blade, flapping modes were dominant. The dynamic aeroelastic method enabled an assessment of the effect of flapping on the blade loads, in conjunction with the effect of tower. Aeroelastic effects were found to be secondary for the MEXICO blade, but had a stronger effect on the larger NREL Phase VI blade.