行波和驻波模式下热声振荡的临界温度梯度

热声机械作为一种能量转化装置。其效率于传统发动机还有较大差距。本文讨论了热声发动机在驻波和行波两种不同工作状态下,其声功率产生的临界温度梯度与流道尺寸和工作介质的关系,得出了两种模式下最佳的工作条件。结果表明;采用行波形式的热声发动机结构,可以有效降低临界温度梯度,提高热致声的效率,同时可以利用一些低品位来做为热声发动机的高温端。     

Open cycle traveling wave thermoacoustics: mean temperature difference at the regenerator interface

In an open cycle traveling wave thermoacoustic engine, the hot heat exchanger is replaced by a steady flow of hot gas into the regenerator to provide the thermal energy input to the engine. The steady-state operation of such a device requires that a potentially large mean temperature difference exist between the incoming gas and the solid material at the regenerator's hot side, due in part to isentropic gas oscillations in the open space adjacent to the regenerator. The magnitude of this temperature difference will have a significant effect on the efficiencies of these open cycle devices. To help assess the feasibility of such thermoacoustic engines, a numerical model is developed that predicts the dependence of the mean temperature difference upon the important design and operating parameters of the open cycle thermoacoustic engine, including the acoustic pressure, mean mass flow rate, acoustic phase angles, and conductive heat loss. Using this model, it is also shown that the temperature difference at the regenerator interface is approximately proportional to the sum of the acoustic power output and the conductive heat loss at this location.     

负载对热声发动机性能的影响

热声发动机作为一种完全没有运动部件的能量转化和传输机械具有广阔的应用前景.为了提高热声发动机的驱动性能,本文采用变负载法对热声发动机性能的影响因素进行了实验研究.实验结果表明,负载的阻力和容抗对热声发动机的加热温度、压比和声功引出有重要影响.同时,实验中还发现了能够使热声发动机瞬时消振和起振的实验方法,将极大方便对热声发动机的开关控制.     

A thermoacoustic-Stirling heat engine: detailed study

A new type of thermoacoustic engine based on traveling waves and ideally reversible heat transfer is described. Measurements and analysis of its performance are presented. This new engine outperforms previous thermoacoustic engines, which are based on standing waves and intrinsically irreversible heat transfer, by more than 50%. At its most efficient operating point, it delivers 710 W of acoustic power to its resonator with a thermal efficiency of 0.30, corresponding to 41% of the Carnot efficiency. At its most powerful operating point, it delivers 890 W to its resonator with a thermal efficiency of 0.22. The efficiency of this engine can be degraded by two types of acoustic streaming. These are suppressed by appropriate tapering of crucial surfaces in the engine and by using additional nonlinearity to induce an opposing time-averaged pressure difference. Data are presented which show the nearly complete elimination of the streaming convective heat loads. Analysis of these and other irreversibilities show which components of the engine require further research to achieve higher efficiency. Additionally, these data show that the dynamics and acoustic power flows are well understood, but the details of the streaming suppression and associated heat convection are only qualitatively understood.     

同轴型行波热声热机的实验研究

自行设计搭建了国际首台同轴型行波热声热机的实验装置 ,以氮气为工质 ,获得频率为1 3 7Hz的谐振声波。回热器热端温度达到 2 0 0℃左右时 ,热声热机开始起振 ,平均振幅 0 .1 4bar     

Observation of traveling thermoacoustic shock waves (L)

Shock waves were explored in the thermoacoustic spontaneous gas oscillations occurring in a gas column with a steep temperature gradient. The results show that a periodic shock occurs in the traveling wave mode in a looped tube but not in the standing wave mode in a resonator. Measurements of the harmonic components of the acoustic intensity reveal a clear difference between them. The temperature gradient acts as an acoustic energy source for the harmonic components of the shock wave in the traveling wave mode but as an acoustic energy sink of the second harmonic in the standing wave mode.     

行波管电子枪热分析与结构优化设计

利用ANSYS软件建立某Ka波段行波管2 mm阴极电子枪的有限元模型,并进行稳态及瞬态热分析,提取热流矢量图与温度分布图,得到阴极稳态时的温度分布及预热时间。对电子枪样品进行实验测试,得到的实测温度与模拟温度相差2%,因而在误差允许的范围内有限元方法是可行的。根据热流矢量图对热屏蔽筒进行结构优化,优化后,阴极温度比优化前提高了28 ℃,整枪最高温度提高了27 ℃,阴极预热时间缩短了40 s,缩短幅度达到33％。优化后的结构较大程度地提高了阴极的快启动性能,提升了行波管的快速反应能力。     

Experimental investigation of a 25-MW microwave (3-cm range) compressor prototype

An experimental study of a resonance microwave (3-cm-range) compressor with gas insulation and energy output through a superdimensional coaxial interference switch is reported. The rated parameters of the compressor are output signal power ∼25 MW, signal duration 2 ns, gain 26 dB, and efficiency ∼57%. A gain of 20 dB was achieved at a peak output signal power of 12 MW, signal duration of 2 ns, efficiency of ∼24%, and traveling wave power of 24 MW.     

基于黄金分割搜索算法的行波管测量方法

为了提供声学材料的测试环境,该文通过有源吸声技术在行波管中建立了一套测量系统,声管中实现了模拟无限水域的行波场环境,从而对样品的声学参数进行测量。提出了一种利用黄金分割搜索算法对最佳时延与幅值进行搜索从而完成行波场建立的方法。在上述行波场建立的基础上,利用双水听器法分别对水柱与钢板样品的声学参数进行了声学测量,透射系数测量值与理论值符合较好。该方法为声学参数的测量方法提供了有意义的参考。     

回旋行波管低加热功率阴极的研究

为降低回旋行波管阴极的加热功率,采用支持筒切缝和支持筒外加热屏的阴极结构,运用ANSYS有限元软件对该结构的切缝数目和切缝深度进行优化计算,并分析切缝和加热屏对阴极发射带温度分布的影响;给出了阴极发射带温度和切缝数目、切缝深度的关系。在发射带同等温度条件下,对比优化结构和原结构的加热功率。结果表明,改进后的结构使得加热功率下降了约40%, 大大降低了阴极的加热功率,为高性能回旋行波管热阴极的研制提供了一定的参考。     

脊加载螺旋槽行波管的小信号增益计算

脊加载螺旋槽行波管是一类新型毫米波大功率器件,给出了此结构中引入电子注后的“热”色散方程,并利用“牛顿”下山法求解了此复系数超越方程.通过数值计算给出了一个工作电压为20kV频率为474GHz的脊棱加载慢波结构的具体尺寸,并对此结构中小信号增益随脊尺寸的变化情况及电子注参数对其影响进行了研究,计算结果表明：此结构适宜于作为高增益窄带毫米波大功率行波管的慢波线,其3dB增益带宽为34%;为了展宽其工作带宽,可以适当减小间隙宽度,也可在一定范围内提高电子注电流.给出的理论对于研制此类行波管具有一定的指导意 关键词：     

140GHz大功率交错双栅行波管的设计和模拟研究

采用交错双栅结构,结合带状电子注,研究了一种工作在140 GHz频段的大功率行波管. 本振模数值计算表明该结构具有良好的色散特性和耦合阻抗.针对所采用的慢波结构, 提出了慢波过渡结构、输入输出耦合器和集中衰减器,保证了行波管的良好工作. 利用三维大信号模拟计算的方法得到的结果显示,当电子注直流功率为5.115 kW,输入信号功率为0.1 W时, 所研究的行波管能在132-152 GHz范围内提供大于300 W的峰值功率,其中在138 GHz时得到最大功率546 W, 对应增益为37.37 dB.当在0.027-0.46 W内调节输入信号功率,可以保持该行波管在128-152 GHz 频带内得到大于440 W的峰值功率,对应的电子效率大于8.6%. 结果显示该行波管将在大功率短毫米波领域具有重要意义和潜在应用价值.     

考虑谐波互作用的行波管欧拉非线性理论模型

基于拉格朗日体系的考虑谐波互作用的理论模型,将离散的粒子近似处理为流体,得到电子相位的连续分布函数.对电子相位连续分布函数进行傅里叶一阶展开,并结合贝塞尔母函数关系式,建立了考虑谐波互作用的欧拉非线性理论模型.应用考虑谐波互作用的欧拉非线性理论模型对一支L波段空间行波管和一支C波段空间行波管进行大信号分析,并与拉格朗日理论模型进行对比.结果表明:在增益1dB压缩点之前,考虑谐波互作用的欧拉非线性理论模型与拉格朗日理论模型十分符合,增益最大误差不超过4%.考虑谐波互作用的欧拉非线性理论模型能够有效的对增益1 dB压缩点之前的谐波进行分析.仿真结果验证了考虑谐波互作用的欧拉非线性理论模型的正确性和有效性.考虑谐波互作用的欧拉非线性理论不但提供了一个谐波快速计算模型,而且为后续研究行波管谐波的产生机理与抑制方法奠定了基础.     

Analysis of the instability in relativistic traveling wave tube

The relativistic traveling wave tube is an important high power microwave source. The corrugated cylindrical waveguide is usually used as slow wave structure of this device. Starting from wave equation and using boundary conditions, dispersion relation is derived for the corrugated waveguide, in which an intense relativistic electron beam propagates along the axis. Two cases which are shorter period and longer period are discussed in this paper respectively. The small signal gain of the relativistic traveling wave tube is analyzed and some conclusions are drawn. The analysis method presented in this paper can be extended to other types of slow wave structures of relativistic traveling wave tube.     

线性与非线性传热过程的Curzon-Ahlborn热机在任意功率时的效率

热机性能的优化是热力学领域的一个重要问题,而工质与热源之间的传热过程是热机工作时产生不可逆的主要来源.本文在引入功率增益和效率增益两个重要参数的基础上,基于一个简化的Curzon-Ahlborn热机模型并利用合比分比原理,给出了线性与非线性传热过程的热机在任意功率输出时的效率表达式,结合数值计算详细讨论了热机在任意功率输出时的特性.研究表明,参数ξ作为功率增益δP的函数存在两个分支:在第一分支上(不利情形),效率呈现出单调变化特征;在第二分支上(有利情形),效率随着的δP变化是非单调的且有最大值.随着传热指数的增加,热机的工作区域减小,这源于非线性传热过程包含热辐射所致.进一步发现功率-效率关系曲线存在权衡工作点,热机在该点附近工作能够实现最有效的热功转换.研究结果有助于深入理解具有不同传热过程热机的优化执行.     

Application of an acoustic noise removal method to aircraft-based atmospheric temperature measurements

An acoustic noise removal method is used to reject engine acoustical disturbances from aircraft-based atmospheric temperature measurements. Removal of engine noise from atmospheric temperature measurements allows a larger wave number range to be fit while quantifying the magnitude of atmospheric temperature turbulence. The larger wave number range was found to result in a more statistically certain spectral slope estimate, with up to a 50% reduction in the standard deviation of measured spectral slopes. The noise removal technique was found to break down under conditions of weak atmospheric temperature turbulence where the engine acoustical disturbance can be several orders of magnitude larger than atmospheric temperature turbulence.     

高梯度行波电子直线加速器

本文评述了一种采用射频功率反馈的高梯度行波电子直线加速器,详细计算了它们的能量增益和瞬态特性。最后简要地比较了它与高梯度驻波直线加速器的性能及特点。     

Impact of pressure fluctuations on the dynamics of laminar premixed flames

Thermo-acoustic instabilities are problematic in the design of continuous-combustion propulsion systems such as gas turbine engines, rocket motors, jet engine afterburners, and ramjets. Conceptually, the coupling between acoustics and flame dynamics can be divided into two categories: flame area fluctuations and changes in the local flame speed. The latter can be caused by the thermodynamic fluctuations that accompany an acoustic wave. This coupling is the focus of the present work. In this paper, we are concerned with the dynamics of laminar premixed flames involving large hydrocarbon species. Through high-fidelity numerical simulations, we investigate the flame response for a wide range of fuels and acoustic frequencies. The combustion of hydrogen and methane is considered for verification purposes and as baseline cases for comparison with two large hydrocarbon fuels, n-heptane and n-dodecane. We extract the phase and gain of the unsteady heat release response, which are directly related to the Rayleigh criterion and thus the stability of the system. For all fuels, we observe a local peak in the heat release gain. At high frequencies, we find that the fluctuations of the different species mass fractions decrease with the inverse of the acoustic frequency, leading to chemistry being “frozen” in the high-frequency limit. This allows us to predict the flame behavior directly from the steady-state solution.     

W波段回旋行波管放大器的模拟与设计

回旋行波管放大器是高功率毫米波雷达发射系统最重要的候选者.通过对回旋行波管放大器中的绝对不稳定性、回旋返波振荡以及电子注-波互作用的研究，讨论了回旋行波管的稳定性、寄生模式的抑制和工作参数的优化等问题，给出了W波段TE₀₁模回旋行波管放大器的模拟设计结果.PIC粒子模拟结果表明，在电子注电压100kV、电流10A、工作磁场3.52T时，94GHz的基波回旋行波管放大器可获得大于250kW的输出功率、40dB的增益、大于25％的效率和约5％的带宽. 关键词： W波段 回旋行波管放大器 模拟 设计     

热声热机热声核内传热与流动特性实验研究

本文通过搭建扬声器驱动的热声热机可视化实验台,利用粒子成像测速仪(PIV)和红外热像仪得到冷、热端换热器间速度及温度场分布,对有无声场两种情况下热声核中速度及温度场的变化进行了实验研究。实验结果表明,外加声场改变了热声核中热对流的基本模式,增强了冷热端换热器间的换热能力,对热声核中的温度分布有着显著的影响。揭示了热声核中的流动与换热规律。