纤维悬浮湍流的方程和解及其在管流中的应用

推导了纤维悬浮流的平均运动方程和纤维平均取向角的概率密度函数方程，提出了计算纤维平均取向角分布和悬浮流平均量与脉动量关联函数的逐级迭代方法。将推导的方程和提出的方法用于纤维悬浮管流场的计算并进行了相应的实验，计算和实验结果吻合很好。研究结果表明，在相同的压力降下，与没有纤维的牛顿流相比，纤维悬浮流具有较大的流量，因而纤维在流场中起着减阻的作用，减阻的量随着纤维浓度的增加而增大。在相同情况下，纤维悬浮流的相对湍流强度和雷诺应力比牛顿流小，这说明纤维能够抑制湍流，抑制的量与纤维的质量浓度成正比。     

非正交座标S_1流面流函数跨音松弛计算

本文在吴仲华教授的叶轮机械三元流动理论的基础上,推导了非正交曲线座标系下的叶轮机械流函数方程及有限差分方程的通用形式.这些方程可用于平面、任意迥转面及任意翘曲的S_1或S_2流面的跨音及亚音流场计算。数值求解中采用了混合差分格式线松弛计算方法。采用了密度预测法由流函数值唯一确定了密度值,解决了流函数方程求解跨音流场的困难,用此方法编制了计算机程序并作了计算,所得结果与实验结果比较一致。     

湍流模型在内流流场数值模拟中的应用

本文将Spalart-Allmaras湍流模型方程推导为守恒形式,并应用于内流湍流流场计算.采用此-方程湍流模型分别对扩压器流场以及NASA 67转子流场进行了数值模拟.结果表明常用在外流计算中的Spalart-Allmaras湍流模型在内流计算中仍具有较高的精度、数值稳定性和效率.     

一种新的k方程转捩湍流模型

本文在分析了针对充分发展湍流模型建立的k方程湍流模型模拟转捩流动的能力之后，构筑了一种新的Fμ函数及相应的k方程湍流模型．将该模型应用于数值求解NS方程，模拟了中等来流湍流度下零压力梯度平板捩报流动，并将部分计算结果与实验结果及经验关系进行了比较．     

非正交曲线坐标可压湍流S_1流面计算

一、引言 本文在文献[1]的基础上导出了非正交曲线坐标S_1流面内的可压湍流通用流函数方程组,文中连续方程和运动方程直接转化为流函数方程形式,不受势函数的无旋流动的限制,本文用焓和熵代替运动方程中的压力项,直接求解能量方程和熵方程,避免了压力修正带来的困难。导出了非正交曲线坐标系的κ-ε湍流双方程,在近壁区采用壁面函     

跨音透平变工况计算

得到了一组包括S_2流面方程、简化S_1流面方程(用于求解叶栅尾部三角区)、流动损失关系方程及落后角关系方程的联合方程组,此方程组用于计算透平机械的正问题。 考虑了亚临界、临界及超临界流动的本质差别,在阻塞计算中考虑了损失的影响。用一种联合求解的方法来求解此方程组。损失、落后角及其它流动参数是在同一迭代过程中得到的,所以不会发生假堵塞,收敛也快。完成了计算机程序并用于跨音透平非设计性能的计算。 用此程序计算透平级出口性能得到了满意的结果。折合流量、效率及膨胀比与实验结果相当符合,计算结果与实验数据之差在1％之内。     

用谱方法数值模拟槽道内的气固两相流动

在数值模拟领域内,谱方法具有收敛快、分辨率高和精度高的优点．谱方法处理边界方便,随着数值方法的改善和计算机的发展,它在数值模拟中的作用愈加重要．这里采用谱方法数值求解三维Ｎ—Ｓ方程,用这一方法计算了直槽道内流体的流动．计算得到的层流和湍流结果与理论结果符合地较好．在此基础之上进一步模拟了几种不同槽道内的三维粘性流体层流流动,特别在弯曲槽道内的流动计算中,发展了源项处理方法,正确地反映了弯曲固壁对流体流动的影响．通过对湍流计算获得的脉动速度场的统计可以得到湍流运动的许多统计量,正确地反映了湍流运动的特征,说明可以用模拟得到的流场来代替真实的流场．进行了气固两相流动的研究,由直接模拟得到的流体瞬时速度场对固体粒子的作用进行了粒子运动的模拟计算,得到了颗粒在真实流场中运动的浓度,轨道等有用信息和运动特性,得到了令人鼓舞的结果．     

绝热可压湍流的焓熵壁面律

在湍流流场的数值计算中,应用壁函数方法或称壁面律方法处理近壁区的流动已经证明是一种行之有效的方法,这可以减少壁面附近区域的计算工作量。在叶轮机械的流动计算中,常采用克罗柯形式的方程组,这里包含了焓与熵的计算。速度的壁面律已有许多人论述过,焓与熵的壁面律很少有人提及,而熵壁面律的概念首次由本文作者提出。     

用三维流函数求解叶轮机械三维可压流场

采用三维流函数的定义式,本文推导了在任意曲线坐标系下的三维流函数的主方程。由于两个主方程中各自都包含了两个流函数的二阶偏导数,这给数值求解带来不便。针对三维流函数和其方程特性,将两个流函数方程的差分方程视为同时求解两个流函数的二元一次联立方程,采用相应数值计算方法。通过对算例的试算,表明了该数值处理方法是可行的,这使得三维流函数方法可以很好地适用于叶轮机械三维流场的计算。     

一种可压缩湍流RANS模拟的浸入边界方法

提出一种可压缩湍流RANS(Reynolds-Averaged Navier-Stokes)模拟的浸入边界方法。该方法的解重构中,不再定义用于插值的参考点。利用其周围计算内点上已知的流动变量值,解域内紧靠壁面的网格节点上的流动变量通过距离倒数加权方法插值确定。为降低高雷诺数湍流模拟的近壁区域网格分辨率要求,采用一种显式壁面函数将无滑移边界条件转化为无穿透边界条件和当地剪切应力条件;该壁面函数无需迭代求解,提高了计算效率。RAE2822翼型亚、跨音速绕流的数值模拟验证了方法的可靠性。     

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.     

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.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.