随机风况下襟翼闭环载荷控制的数值研究

柔性襟翼在减缓风力机叶片极限与疲劳载荷方面一直备受关注。为研究柔性襟翼在非稳定入流时的减载能力,以二维翼型S809为基础翼型,CFD计算获取的翼型升力为反馈信号,利用ANSYS Fluent 17.0及其用户自定义端口,建立了襟翼闭环载荷控制系统。研究了襟翼在来流随机变化时减缓翼型升力波动的效果,并分析了襟翼最大偏转速度与系统延迟时间对控制效果的影响。结果表明:襟翼控制后的翼型升力波动标准差减小了99%,进一步提高最大偏转速度后,仅在变化较急剧的峰值处略有区别;较大的延迟时间导致升力在波动方式与范围上都有别于无延迟与小延迟,不利于襟翼对载荷波动的减缓。     

梳状散热器结构和角度对大功率LED结温的影响

利用计算流体力学(CFD)软件Fluent模拟了梳状肋片散热器的大功率LED灯的温度场分布。从散热器肋片高度、肋片间距以及灯具的照射角度三方面分析了散热器的散热效果。通过对比分析不同散热器的速度流场与温度场分布,得知当肋片高度为10mm、间距为4.1mm时散热器散热效果最佳。灯具的照射角度也会影响到散热器的散热性能,当照射角为90°时散热器性能最佳。     

扩压叶栅中Gurney襟翼气动作用的实验研究

以NACA65-12(10)叶型为基础,在稠度1.0的平面叶栅上,实验测量了两种高度Gurney襟翼在不同攻角下气动特性。设计工况下,襟翼高度为1%弦长时,升阻比平均提高上升10%;襟翼高度为3%弦长时,升阻比增加16.6%。与原始叶型的叶栅气动特性对比结果表明,随着襟翼高度的增加,叶栅升力先于阻力增加,升阻比先提高后降低,适当的襟翼具有提升叶栅升阻比的作用。     

几种前缘流动控制的实验研究

在低速风洞中，以NACA0012翼型为例，采用对比实验的方法，研究了三种改善翼型大攻角气动性能的流动控制措施，即（1）在翼型上表面安装小三角翼涡发生器；（2）在翼型前缘安装矩形涡发生器；（3）利用前缘切口．实验雷诺数分别为4．9×105到6．5×105，攻角范围为-10°至20°．实验结果表明三种措施均可不同程度地改善原翼型在其失速区域的性能，不仅可以提高翼型的升力，而且可以提高其升阻比；但常用攻角范围内翼型气动性能有不同程度的下降，三种措施各有优缺点．几种前缘流动控制的实验研究@刘宝杰$北京航空航天大学404教研室!北京,1…     

风力机翼型尾缘襟翼动态特性分析

采用计算流体力学方法研究了带有运动尾缘襟翼的风力机翼型,考察了襟翼偏转角频率对翼型气动参数及非定常特性的影响。结果表明:多数情况下,翼型升力系数滞后于偏转角变化,且相位差随着角频率的增加先增大后减小;尾缘襟翼改变升力系数的能力随着角频率的增加而减小;以尾缘襟翼长度为特征尺度定义的襟翼折合频率可作为尾缘襟翼问题非定常特性的判断准则,当该折合频率大于或接近0.01时,流场具有明显的非定常特性。     

无缝襟翼吹气控制机理和地面效应分析

基于Coanda效应的无缝襟翼吹气控制能大幅度提升机翼升力, 改善大型运输类飞机起降性能, 因此研究起降阶段地面效应对吹气控制的影响十分必要。通过数值模拟方法, 从流场变化的角度分析了无缝襟翼吹气控制机理, 以及有/无襟翼吹气时地面效应对翼型气动性能的影响。襟翼吹气使Coanda表面产生局部低压区, 形成指向Coanda表面的压力梯度, 进而引起射流上方的主流偏转和加速, 使整个翼面近壁区产生顺时针方向的速度增量; 翼面压力面的压力增大, 吸力面的吸力增强, 其中主翼上翼面吸力增强是翼型升力增加的主要来源。无吹气时, 地面效应使翼型上/下翼面附近的流速均降低, 上/下翼面的压力均有所提高, 整体上使翼型升力降低。有地面效应时的襟翼吹气增强了下翼面对来流的阻滞作用, 进一步提高了下翼面的压力; 襟翼吹气使上翼面气流加速, 可抵消地面效应引起的上翼面气流减速, 一定程度上减小了地面效应引起的上翼面吸力损失。      

进入轨道偏差对火星科学实验室气动力特性的影响

针对火星科学实验室(MSL)高超声速进入过程,利用三维并行程序求解流体力学Navier-Stokes方程,耦合真实气体模型,分析火星大气中真实气体效应对进入器气动力特性的影响量在进入轨道发生偏差时的变化规律.结果表明:对海盗号的计算结果与飞行数据符合很好,验证了火星大气真实气体模型和计算方法;真实气体效应影响下,激波层厚度大为减小,温度下降明显,进入器阻力系数明显增加,升力系数变化不大,俯仰力矩系数增加,基准状态下配平攻角较完全气体减小约2.2°;高度不变,Ma数增加导致阻力系数和俯仰力矩系数增大,配平攻角和完全气体的差值由1.6°增加到2.6°,表明Ma数变大时真实气体效应引起的气动力变化增强;Ma数不变,高度增加略微减弱波后化学反应,对进入器气动力特性基本没有影响.     

凹槽对风力机叶片尾缘襟翼性能的影响

本文采用单方程S—A湍流模型计算了尾缘襟翼与主体翼型连接处的凹槽对二维翼型气动特性及流场的影响。选用带有30％弦长固定偏斜20°角度尾缘襟翼的NACA0015翼型作为研究对象,分析了流场的相关特性。数值计算结果表明：凹槽对于带有尾缘襟翼的二维翼型气动特性有一定影响,在负攻角及较小正攻角时,减小翼型升力系数;随着攻角增大...     

低对称性非线性光学晶体硼酸铋(BIBO)的1064nm三倍频性质

采用高温溶液法成功生长出高光学质量的硼酸铋 (BIBO)晶体 ,尺寸达到 2 4mm× 19mm× 35mm ,质量为4 8g。对BIBO晶体进行了定向 ,并测量了该晶体的主轴折射率。讨论了BIBO晶体的 10 6 4nm三倍频性质 ,包括相位匹配角、有效非线性光学系数deff、容限角、走离角等。结果表明 ,BIBO晶体的最佳三倍频方向为 (137.7°,130°) ,其有效非线性光学系数值达到 3.6 0 pm/V ,属I类相位匹配。就主平面内的相位匹配方向而言 ,(14 6 .4°,90°)具有最大的有效非线性光学系数值 ,为 3.16pm/V。在 10 6 4nm的腔外三倍频实验中 ,(14 6 .4° ,90°)BIBO晶体的转换效率达到 39.5 % ,角度容限半宽为 0 .2 2mrad·cm ,该数值与 0 .175mrad·cm的计算值基本符合。由于(33.6°,90°)BIBO晶体的有效非线性光学系数较小 (0 .31pm/V) ,其三倍频转换效率小于 5 %。     

气压对吸气式激光推进冲量耦合系数的影响

 保持CO₂激光的单脉冲能量为61.4~64.6 J，采用高精度冲击摆系统进行了不同气压下吸气模式激光推进冲量耦合系数的实验测试，分析了对应的高度特性。结果表明：气压为2.8×10⁴～1×10⁵ Pa，即距离地面0～10 km时，冲量耦合系数大约3.5×10^-4 N·s·J^-1，上下波动幅度低于5%；气压低于2.8×10⁴ Pa，即高度大于10 km时，冲量耦合系数呈二次曲线显著下降；当气压降至1×10³ Pa，即距离地面约31 km高度时，耦合系数仅为9.7×10-5 N·s·J^-1。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.