跨音速轴流压气机级三维粘性流场全工况数值模拟

采用一种快速求解三维粘性流场的计算方法求解跨音速轴流压气机级内部流场及全工况特性。该方法以LU-SGS-GE隐式格式和MUSCL TVD迎风格式为基础,结合壁面函数方法和简单的混合长度湍流模型,对三维可压缩雷诺平均Navie-Stokes方程进行求解。叶列间参数的传递采用混合平面方法并应用了微机网络并行计算技术。计算得到了NASA 37号低展弦比、跨音速轴流压气机级70％设计转速下的全工况性能曲线,并重点分析了其中一些典型工况下的内部流场。计算与实验结果的对比表明此方法能快速得到三维粘性流场的流动特性且计算精度较高,可用来模拟跨音速轴流压气机级内的全工况三维粘性流动。     

混流式水轮机内部流场的三维空化湍流计算

本文通过理论分析,引入三维混合流体完整空化湍流模型,确定了混流式水轮机内部三维空化湍流计算的方法.用数值模拟手段对混流式水轮机的内部空化流场进行了计算,采用了全三维全流道的湍流计算方法,基于RNG的k-ε湍流模型和SIMPLEC算法,从蜗壳进口到尾水管出口,包含所有流道在内的整体一次完成定常.根据得到的三维空化流场数据,对转轮内部流场进行了流场分析,求得了计算临界空化系数,和试验值进行了比较;模拟了特征工况下的尾水管涡带,和试验数据进行了比较.     

泵站水泵进水池内防涡装置有效性的数值验证

本文提出了一种消除泵站水泵吸水管内旋涡和流动分离的圆锥形防涡装置。为了验证该装置的有效性,建立了泵站水泵进水池和吸水管内三维湍流流场的数学模型,用分区网格构造了泵站水泵进水池和吸水管的贴体计算网格,采用有限体积方法,计算了无圆锥形防涡装置和有圆锥形防涡装置时,水泵进水池和吸水管内三维湍流流场,结果证明该圆锥形防涡装置能有效消除水泵吸水管内旋涡和流动分离。     

汽车水泵性能三维数值模拟及结构改进

考虑到汽车水泵进出口管和蜗壳,对某型汽车水泵进行了全三维流场数值模拟.分析数值模拟结果与试验测试结果的差异,说明该水泵的蜗壳与叶轮不匹配,造成整机性能恶劣.对该泵内部的流场和总压变化过程的进一步分析,提出了减小叶轮出口安装角,扩大扩散管截面积,采用蜗壳高度渐变的改进措施.改进后的水泵进行整机模拟并进行性能预测,表明改进后的水泵性能大大改善.经过实验测试的结果与计算结果吻合,说明改进措施有效,数值计算模型合理.     

低展弦比跨音速轴流风扇转子流场三维数值模拟

应用基于时间推进的有限差分法求解跨音速压气机风扇转子内部三维粘性流场．该方法以新型ＬＵ隐式格式和改良型 ＭＵＳＣＬ ＴＶＤ格式为基础,对三维可压缩雷诺平均 Ｎａｖｉｅ－Ｓｔｏｋｅｓ方程和低雷诺数ｑ－ω双方程湍流模型进行求解．计算得到了ＮＡＳＡ Ｌｅｗｉｓ ６７跨音速、低展弦比轴流风扇转子的性能曲线并重点分析了近最高效率点工况和近失速工况下的内部流场．计算与实验结果的对比表明此方法能够得到三维粘性流场的流动特性且计算精度较高,可用来模拟跨音速风扇转子内部流动．     

径向导叶对混流式核主泵水力性能的影响

基于三维不可压缩流体的N-S方程和RNG k-ε湍流模型,采用流体计算软件ANSYS-Fluent对设计工况下,不同导叶数及导叶进口边位置的混流式核主泵水力模型的三维湍流流场进行了数值模拟,研究了导叶进口边位置及导叶数对混流式核主泵模型水力性能的影响。计算结果表明:随着导叶数的增加,当导叶数为奇数时,泵的计算扬程和水力效率值都有所增大,且水力效率值增大的趋势在减小;导叶数为偶数时,泵的计算扬程和水力效率值先减小后增大,在导叶数为16片时,泵的计算扬程和水力效率值最小。随着导叶进口边与叶轮出口边夹角θ的增大,泵的计算扬程和水力效率值先增大后减小,当θ=14°时,模型泵的水力性能最好。研究结果可用来了解混流式核主泵水力模型的内部流场特征,并为其高效水力模型优化设计提供有益参考。     

某双级风扇亚音工况下流动失稳诱因分析

以一带减振阻尼台的双级风扇为研究对象,对其亚音工况下的内部流场进行了更为真实的全三维数值模拟。通过对比分析计算和试验的总性能和基元性能可以看出,计算结果很好地再现了试验给出的流动信息。以此为基础对其内部流场进行了详细分析,结果表明第1级动叶叶顶吸力面附面层分离形成的低能气团及其造成的流动堵塞是该双级风扇亚音工况下流动失稳的诱发因素。     

微射流放大器内部三维流动数值模拟

采用三维流动求解器CFD-ACE ,以水作为工作介质,对不同流动工况的偏向型微射流放大器内部三维流场进行了数值模拟,得到了流场的压力分布图和速度矢量图,并通过计算得到平均流量增益曲线,将偏向型微射流放大器内部流场分析与外部运行特性分析有机地结合起来,为实验方案的优化提供了依据。     

轴流泵端壁区域流动三维粘性数值计算

本文采用通用流场分析软件FLUENT,基于N-S方程,选用RNG κ—ε湍流模型与SIMPLEC算法,对轴流泵叶轮内部(及端壁间隙)流动进行了三维粘性数值计算。通过实验验证,表明数值计算结果和实测数据吻合较好。详细分析了叶顶附近流场形态以及叶轮出口轴向、周向速度分布,进行了性能预估。并给出了实验装置图。     

不同离散格式下的离心泵内部流动数值模拟研究

为研究离散格式对离心泵性能预测精度的影响,本文以自吸式离心泵为计算模型,采用Realizableκ-ε湍流模式进行三维内流场的数值模拟研究,分析了从零流量到最大工作流量下的内部流动和水力性能。建立了考虑内部间隙影响的自吸式离心泵全三维计算模型,分析了动量方程对流项采用一阶差分和二阶差分格式对计算精度的影响,同时分析了压力项的Standard和PRESTO离散格式对计算精度的影响。结果表明,在小流量工况下,采用二阶迎风格式具有较高的计算精度,而在大流量工况下采用一阶迎风格式更为合适。该结果可为准确预测离心泵全工况外特性提供参考依据。     

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.