行波热声发动机容腔管和反馈管的调相作用研究

带环形圈的热声发动机是一种新型的行波型热声发动机,由于能够在环形圈内回热器附近调制出行波相位,因此具有比驻波发动机更高的效率。环形圈的反馈管和180度弯管分别在系统中起着感和容的作用,在相位的调制过程中它们起着至关重要的作用,尤其是对于感的作用比较强的小型系统,它们的作用更加突出。该文通过计算,分析了小型行波热声系统中感和容对于回热器入口处和回热器中心位置处的压力波动和体积流率相位的调制作用,以及这种调制作用对于效率,压力波动的幅值的影响。     

运用功能梯度结构降低大功率激光系统中镜面热变形的数值分析

 提出一种运用功能梯度结构以有效降低大功率激光系统中镜子温度和镜面热变形以及减缓热应力的新方法。讨论了环形分布和高斯分布2种类型的激光源。有限元分析结果表明，通过这种方法可使硅镜和铜镜的表面热变形成倍降低，并且还能同时显著降低镜体温度。讨论了代表热学和力学性质的函数表达式的斜率对镜面热变形的影响，研究表明：功能梯度结构的热物理对镜面形变产生重大影响，而力学性质对镜面形变的影响非常小。该结论可为具有该功能梯度结构的镜子优化设计和制造提供参考。     

弱非线性热声理论模型的建立及简化

本文指出非零的周期平均热声效应在本质上是非线性的,应保留到二阶精度。在小振幅条件下,利用摄动方法,以无限大平板流道为例,建立了二阶精度的弱非线性热声理论模型,并在不同条件下对模型做了进一步简化。这一理论为理解热声系统的工作机制以及设计优化热声系统提供了强有力的理论工具。     

环形孔径高斯光束的远场特性

 讨论了环形孔径高斯光束的远场光斑能量分布,并给出了拟合表达式。首先推导了光束没有抖动时远场光斑的光能分布表达式,然后研究了各种不同中心遮拦和不同光束截断比, 在有以及没有激光束抖动的情况下,对高斯光束的远场环围能量的分布变化的影响。     

双光子光声效应理论

对双光子光声效应作了系统的理论分析，导出了双光子光声效应的波动方程，并求出双光子光声信号的表达式。 关键词：     

多扇环形结构永磁多极系统的二维场形分析

根据“均匀磁化”原理,利用谐波分析方法,对多扇环形结构永磁多极系统(L→∞)的场形进行了分析,并得到了二维解析表达式。分析了两种情况:一种是固定场强多极系统,二是场强可调的多极系统。     

多扇环形结构永磁多极系统的三维场形分析

本文根据“均匀磁化”原理,利用谐波分析方法对一种新型结构的多极系统——多扇环形结构永磁多极场的场形进行了计算,得到了三维的解析表达式。用它可计算多极系统任一截面的磁场形态。     

非均匀加宽单模激光器的最佳透射率

给出四能级系统非均匀加宽单模激光器最佳透射率的表达式和分布曲线,并与均匀加宽单模激光器最佳透射率进行了比较.叙述了非均匀加宽单模激光器的特点.     

渐变截面热声波导管内的声流解析模型

建立了二维渐变截面热声波导管内的声流模型,分别考虑了封闭直管和环形回路两种不同结构,获得了更为普适的解析结果。封闭直管结构的声流结果可应用于任意宽度的波导管,环路结构的结果考虑了渐变截面管段宽度远大于热、黏穿透深度的情形。研究结果表明,渐变截面热声波导管内的声流主要受声场结构、截面变化及轴向时均温度分布的影响,在其它参量不变时声流量值及分布随波导管特征尺度的不同而变化。该解析模型可应用于热声及其它物理背景下的声流分析。      

透过式光纤陀螺偏振特性的分析

偏振波动是谐振式光纤陀螺(R-FOG)的主要噪声之一,它对信号检测精度具有重要影响。通过矩阵法得到了透过式R-FOG中由偏振波动引起的系统零漂与偏振噪声相关参数、环形谐振腔结构参数间的关系表达式。在一定的透过式R-FOG系统结构参数下,对上述解析表达式进行了数值拟合,通过估算可满足高精度透过式R-FOG系统对偏振相关参数的要求,为偏振波动噪声的理论分析和R-FOG系统的实际搭建提供了理论基础。     

Investigation of azimuthal staging concepts in annular gas turbines

In this work, the influence of azimuthal staging concepts on the thermoacoustic behavior of annular combustion chambers is assessed theoretically and numerically. Staging is a well-known and effective method to abate thermoacoustic pulsations in combustion chambers. However, in the case of, for example, fuel staging the associated inhomogeneity of equivalence ratio may result in increased levels of NO_x emissions. In order to minimize this unwanted effect a staging concept is required in which the transfer functions of the burners are changed while affecting the equivalence ratio as little as possible. In order to achieve this goal, a theoretical framework for predicting the influence of staging concepts on pulsations has been developed. Both linear and nonlinear analytical approaches are presented and it is shown that the dynamics of azimuthal modes can be described by coupled Van der Pol oscillators. A criterion based on the thermoacoustic coupling strength and on the asymmetry degree provides the modal behavior in the annular combustor, i.e. standing or traveling waves. The model predictions have been verified by numerical simulations of a heavy-duty gas turbine using an in-house thermoacoustic network-modeling tool. The interaction between the heat release of the flame and the acoustic field was modeled using measured transfer functions and source terms. These numerical simulations confirmed the original theoretical considerations.     

Analytic model of acoustic streaming in thermoacoustic waveguides with slowly varying cross-section

An analytic model of acoustic streaming generated in two-dimensional thermoa-coustic waveguides with slowly varying cross-section was developed for more general applications. The analytical solutions of acoustic streaming characteristics in the closed straight tube and the annular tube are given based on the model.The solution for the closed straight tube can be applied to the case with any transverse scale.The solution for the annular tube is obtained under the assumption that the width of the varying cross-section part is much larger than the viscous and thermal penetration depths.The effects of cross-section variation,time-averaged temperature distribution and components of sound field are reflected in the analytic solutions. The magnitude and distribution of acoustic streaming velocity vary with the characteristic scale of the waveguides.The analytic model of acoustic streaming can be applied in research under thermoacoustic and other physical backgrounds.     

A study of the optical transfer function for annular binary filters

The annular binary pupil filters consist of two transparent annuli obstructed by an annular mask. The optical transfer functions for them are analytically derived under paraxial approximation, and three- and two- as well as one-dimensional numerical plots are presented. It is shown that by changing the parameters of transparent regions it is possible to improve the axial resolution whilst the transverse resolution remains unchanged, compared with an annular lens. Results indicate, as is well known, that this kind of filters can be applied to three-dimensional confocal microscopy.     

An analytical study of the flame dynamics of a transversely forced asymmetric two-dimensional Bunsen flame

Combustion instabilities in annular combustors are of great interest because of their industrial relevance. Azimuthal acoustic modes, which involve transverse acoustic forcing to flames, have become a key process related to annular combustor instabilities. Transverse mean flow may be a factor that affects azimuthal oscillations. This paper provides an analytical model for a transversely forced two-dimensional Bunsen flame under transverse mean flow. The model is established using a low-amplitude perturbation assumption applied to a G-equation formulation. Forced flame displacement and flame transfer functions (FTFs) are calculated. The results are verified based on numerical solutions of the G-equation. Effects of frequency, transverse mean flow velocity and vertical mean flow velocity on the FTFs are discussed. The symmetric flame without transverse mean flow has a vanishing response to transverse acoustic forcing, while asymmetric flames, which are formed with transverse mean flow, have a bandpass response to transverse forcing. The response at very low and high forcing frequencies is small, with higher transfer function gains only in a certain frequency range. This bandpass response, which is inherently linked to the asymmetry of the flame, is an important factor to account for when considering the flame dynamics related to transverse acoustic effects.     

Acoustic streaming related to minor loss phenomenon in differentially heated elements of thermoacoustic devices

It is demonstrated that the differentially heated stack, the heart of all thermoacoustic devices, provides a source of streaming additional to those associated with Reynolds stresses in quasi-unidirectional gas flow. This source of streaming is related to temperature-induced asymmetry in the generation of vortices and turbulence near the stack ends. The asymmetry of the hydrodynamic effects in an otherwise geometrically symmetric stack is due to the temperature difference between stack ends. The proposed mechanism of streaming excitation in annular thermoacoustic devices operates even in the absence of thermo-viscous interaction of sound waves with resonator walls.     

热声系统的声功测量方法

声功测量对热声系统的研制开发具有重要意义。文中着重介绍了几种声功测量方法 ,阐述了各种方法的测量原理、仪器装置、应用特点及实用范例 ,对于热声系统中声功的测量具有一定参考价值。     

高效室温行波热声制冷的研究 第一部分 方案及热力分析

文中对简化的热声网络法、T型传输线网络法以及传输矩阵法进行了比较讨论。采用简化的热声网络法对几种可能的制冷流程进行了分析 ,并确定出了可能高效工作的制冷方案。最后基于传输矩阵法对一种行波热声制冷机进行了分析和热力设计 ,得到该制冷机较优的结构参数。当制冷温度为 - 2 3℃时 ,其 COP可达 2 .86 ,相对卡诺热效率为 5 7%。     

Vibration and stability of a variable thickness annular plate subjected to a torque

The free vibration and stability of a variable thickness annular plate subjected to a torque are analyzed by the Ritz method. For this purpose, the transverse deflection of an annular plate is written in a series of the deflection functions of a uniform thickness annular plate without the action of a torque. The kinetic and strain energies of the plate are evaluated analytically and the frequency equation of the plate is derived by the conditions for a stationary value of the Lagrange functional. The present method is applied to annular plates with two types of radial thickness variation, power law and exponential, and the natural frequencies (the frequency parameters) and the divergence torques are calculated numerically, from which the effects of the varying thickness, inner/outer radii ratio and edge conditions are studied.