多级风扇/压气机三维粘性流场的数值分析

采用叶排间掺混面模型,研究了多级跨音速风扇及压气机三维粘性流动数值模拟问题,利用ＬＵ－ＳＧＳ隐式算法使计算过程快速收敛,通过高分辨率格式改善跨音速流场中激波的分辨率。对某双级跨音速风扇及五级压气机流场进行了计算,双级风扇各状态的计算结果与实验数据吻合较好。     

透平级非设计工况气动性能的数值模拟

采用新型 ＬＵ隐式格式和改良型高阶 ＭＵＳＣＬ ＴＶＤ格式求解全三维雷诺平均的 Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程和 ｑ－ｗ低雷诺数双方程湍流模型,对一台ＮＡＳＡ跨音单级透平在不同工况下的内部流场进行了详细的数值模拟,并与可能得到的实验结果进行了对比。总结了小流量工况下动叶内部流动的分离模式。     

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。     

多级轴流压气机全工况特性数值模拟

采用一种快速求解三维粘性流场的计算方法求解某多级轴流压气机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，使用多重网格迭代加速收敛技术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．首先对一个五排压气机（进口导叶加两级）进行了全工况特性计算，并对计算结果做了详细分析．然后对前三排（进口导叶加一级）进行了全工况特性计算并与五排联赛的计算结果进行了对比，对多级环境对单级性能的影响机理做了初步探讨。     

振荡机翼跨音速非定常粘性绕流的数值计算

以非定常Ｎ－Ｓ方程为主管方程，采用ＬＵ－ＮＮＤ混合差分格式，Ｃ和Ｃ－Ｈ型贴体运动网格，Ｂ－Ｌ双层代数紊流模型，求解绕振荡翼型和三维机翼的跨音速非定常粘性流场，分别计算了ＮＡＣＡ００１２翼型和Ｍ６机翼作俯仰振荡时跨音速非定常粘性绕流流场。研究了非定常绕流的气动特性，部分计算结果和风洞实验值作了比较。     

NASA67跨音风扇级内粘性流场的准定常数值模拟

本文使用商业软件数值研究ＮＡＳＡ６７跨音速两级风扇第一级在近最高效率点和近堵塞工况点的三维粘性流场。对用细网格计算的级内流场进行了细致的分析,揭示了转子中的激波、附面层、间隙涡、分离流动、流动径向掺混等流动现象,给出了转子与静子叶道中的二次流动和能量损失的分布。     

应用隐式SMAC格式计算射流放水阀内部非定常不可压粘性流场

为了分析射流放水阀内部的非定常不可压粘性流场,在一般曲线坐标系下求解了以逆变速度为参数的不可压Ｎ－Ｓ方程和压力椭圆方程。计算采用了基于隐式ＳＭＡＣ格式的有限差分格式。在这种格式中,非定常流场的速度是通过使用Ｃｒａｎｋ－Ｎｉｃｈｏｌｓｏｎ格式,并在每一时间步处以牛顿迭代的方法得到的;而压力椭圆方程是通过使用Ｔｓｃｈｅｂｙｓｃｈｅｆｆ ＳＬＯＲ格式并交替改变计算方向而求解。通过使用交错网格和迎风差分,诸如改进的ＱＵＩＣＫ格式;计算过程中的误差和数值不稳定能够得到有效地控制。计算结果和实验观察得到的流动图谱对比表明,二者十分吻合。     

轴流叶轮机三维粘性非定常流动计算的双时间方法

采用双时间方法研究了单级跨音速压气机的三维非定常粘性流场计算问题,以ＬＵ－ＳＧＳ隐式解法快速获得虚拟时间域的定常解。对某跨音速单级压气机同时进行了双时间方法和显式方法的非定常流数值计算,双时间法与ＬＵ－ＳＧＳ隐式解法相结合的非定常粘流计算模式可以显著地节省计算时间。     

间断Galerkin方法求解跨音压气机转子流场

本文采用间断Galerkin方法求解雷诺平均N-S方程和SA湍流模型方程,采用Roe格式计算无黏通量,混合格式求解黏性通量中的梯度。为防止跨音速流场计算中的数值振荡,采用了TVD限制器和正性修正。计算了跨音速转子NASA Rotor37在设计转速下的变工况流场,得到了与实验吻合良好的结果,表明DG方法在叶轮机械内部流动计算中具有广阔的应用前景。     

采用高分辨率高精度格式求解跨音压气机转子内三维粘性流场

采用一种新型的ＬＵ隐式算法及４－５阶高分辨率ＴＶＤ格式求解了叶轮机械内的三维Ｎ－Ｓ方程和ｑ－ｗ湍流模型。应用几何法与ＰＤＦ方法混合的网格生成程序,得到了ＲＯＴＲＯ３７跨音速压气机转子内的Ｈ型网格,并将数值模拟的结果同ＬＤＶ实验值进行了比较。     

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.     

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.     

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.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

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.