5MW大型风力机气动特性计算及分析

分别采用BEM和CFD方法对NREL 5 MW风力机的气动特性进行计算,通过分析不同风速下各气动参数的变化规律,揭示了大型变速变桨风力机的功率特性和载荷特性。两种计算结果的详细对比和分析表明,高风速时由于雷诺数大幅增加,BEM方法计算的功率和载荷偏大,在采用BEM方法进行大型风力机的气动设计和校核时,应当考虑雷诺数的影响。同时,失速延迟修正和叶尖损失修正模型在高风速时有较大误差,有必要深入验证传统的修正模型在大型风力机上的适用性。     

2 μm单掺Ho固体激光器及ZnGeP2晶体应用于中长波输出的研究进展（特邀）

2 μm、中波红外3~5 μm及长波红外8~12 μm波段的激光处于大气传输窗口,在激光医疗、环境监测、激光雷达、化学遥感和红外对抗等领域有着非常广阔的应用前景。基于非线性频率转换技术,采用非线性光学晶体在实现中长波红外固体激光输出方面具有结构简单、宽调谐和高功率等技术优势。尤其是使用2 μm单掺Ho固体激光器泵浦ZnGeP₂晶体,在3~5 μm和8~10 μm中长波红外输出中性能优异。在平均输出功率方面,目前可达到102 W@3~5 μm、12.6 W@8.2 μm以及3.5 W@9.8 μm的输出水平,光束质量M2均小于3,其中中波的光光转换效率可达60%。文中针对2 μm单掺Ho固体激光器及ZnGeP₂晶体在中长波输出方面进行了总结。     

Improvement of laser damage thresholds of fused silica by ultrasonic-assisted hydrofluoric acid etching

Polished fused silica samples were etched for different durations by using hydrofluoric(HF) acid solution with HF concentrations in an ultrasonic field. Surface and subsurface polishing residues and molecular structure parameters before and after the etching process were characterized by using a fluorescence microscope and infrared(IR) spectrometer, respectively. The laser induced damage thresholds(LIDTs) of the samples were measured by using pulsed nanosecond laser with wavelength of 355 nm. The results showed that surface and subsurface polishing residues can be effectively reduced by the acid etching process, and the LIDTs of fused silica are significantly improved. The etching effects increased with the increase of the HF concentration from 5 wt.% to 40 wt.%. The amount of polishing residues decreased with the increase of the etching duration and then kept stable. Simultaneously, with the increase of the etching time, the mechanical strength and molecular structure were improved.     

KBrO3在高压下拉曼光谱和结构的研究

利用原位高压拉曼散射和X射线衍射技术,研究了KBrO3在高压下晶格振动和晶体结构演化行为.最高压力达30.9 GPa.通过拉曼光谱发现,在高压下拉曼峰位除了单调移动,没有其它变化,表明KBrO3在研究的压力范围没有发生相变.原位高压X射线衍射实验数据显示,其在高压下依然保持常压的六方结构.通过进一步分析,分别得到了体弹模量B0=25.9(2) GPa(B′0=5.68(0.38))和部分拉曼峰的Grüneisen参数.     

凝胶老化对镱铝共掺SiO_2粉晶化和光谱性能的影响EI北大核心CSCD

采用SiCl_4水解法制备了镱铝共掺石英光纤纤芯原料粉,在O_2氛围下1100℃烧结除羟基处理后,原料粉析出了α-石英相。对镱铝共掺硅酸凝胶进行了常温老化和高压釜高温高压老化处理。测试结果表明,老化处理有效地抑制了镱铝共掺石英玻璃原料粉的析晶行为,Yb^(3+)的荧光强度和荧光寿命得到提高,说明高压釜处理可缩短老化处理时间并提高荧光性能,是制备镱铝共掺石英玻璃原料粉的重要工艺。     

1＋1/2对转涡轮高压动叶顶部间隙流场数值研究

本文对1 1/2对转涡轮中高压动叶顶部间隙中的流动进行了详细的数值研究.通过分析沿弦向不同位置截面上的相对马赫数、速度矢量及静压等的分布,研究了高压动叶间隙及附近的波系及涡系分布.由于1 1/2对转涡轮高压动叶为缩放型流道,其间隙中出现了明显的超音流动,这与普通涡轮间隙中的流动存在明显不同.     

双氙灯光源积分球日照计校准系统

为解决旋转热释电日照计(RPSDR)室外校准易受环境影响、重复性差、效率低等问题,提出了一种以双氙灯光源积分球系统校准RPSDR的室内校准方法。根据RPSDR的组成、结构和测量原理,利用太阳模拟、积分球环境模拟等技术,设计了以氙灯太阳模拟器输出直接辐射、以穹顶氙灯模拟散射辐射的双光源积分球日照计校准系统,提出了积分球结构参数,分析了氙灯光源的辐照度分布和光谱修正,建立了在室内进行日照阈值校准、在室外进行日照时数验证的综合性RPSDR校准方法。经测试,校准系统的有效辐照面内的辐照度均匀性含中心点时为2.5%,不含中心点时为1.6%,有效辐照面内每小时的阈值点辐照度稳定性为0.68%,光源匹配AM1.5 A级太阳光谱能量分布;对一台RPSDR进行室内阈值校准和室外日照时数比对实验,结果验证了经系统校准后的RPSDR测量的日照时数与直接辐射表测量的日照时数参考值的相对误差不超过1%,绝对误差不超过0.26 h,满足气象行业日照时数的观测要求。     

Study on measurement technology of ultra-low brightness北大核心CSCD

光亮度是表征发光体的重要光度特性参数。提出了一种超低亮度计的设计方法,描述了超低亮度计的工作原理和组成;利用微弱光信号处理技术、非线性校准技术、制冷散热技术等实现了超低亮度的自动测量;根据亮度计的测量原理,对仪器进行了标定,测量不确定度达到5%。超低亮度计可适用于实验室和现场等测试场所,为微光夜视装备、显示系统、特种光源、发光材料等的性能评估测试和校准提供计量保障。     

精密红外辐射计测量模块研究北大核心CSCD

红外辐射计用于红外热像仪测试设备的校准。介绍了一种用于红外辐射计的测量模块及方法。设计了采样保持的测量方案,通过参考信号生成采样脉冲,并将采样点设置在每个信号周期的1/4相位处,能显著提高微弱信号的测量能力。对于35℃的黑体辐射信号,通过与现有方案的对比实验,测量信号强度可提高57.6%;在红外热像仪测试设备背景温度为22℃条件下,通过与现有仪器的对比测试,测量信号精度可提升50%以上。     

Oscillator strength study of the excitations of valence-shell of C2H2 by high-resolution inelastic x-ray scattering

The oscillator strengths of the valence-shell excitations of C₂H₂ are extremely important for testing theoretical models and studying interstellar gases. In this study, the high-resolution inelastic x-ray scattering (IXS) method is adopted to determine the generalized oscillator strengths (GOSs) of the valence-shell excitations of C₂H₂ at a photon energy of 10 keV. The GOSs are extrapolated to their zero limit to obtain the corresponding optical oscillator strengths (OOSs). Through taking a completely different experimental method of the IXS, the present results offer the high energy limit for electron collision to satisfy the first Born approximation (FBA) and cross-check the previous experimental and theoretical results independently. The comparisons indicate that an electron collision energy of 1500 eV is not enough for C₂H₂ to satisfy the FBA for the large squared momentum transfer, and the line saturation effect limits the accuracy of the OOSs measured by the photoabsorption method.