格子气的声振荡衰减

采用格子气数值方法模拟了共振腔中气体声振荡衰减过程．计算结果表明：格子气中声振荡衰减的规律和经典理论结果一致；衰减系数随频率增加而减小，并且随密度增加而减小．该结果可以用来说明一些大学统计物理教科书中的一个经典例子存在不完善之处．本中采用了一种新的扭转9-bit格子气模型和并行计算方法，这些结果对今后研究格子气中的热声问题有参考价值．     

热声发动机的优化计算设计

把改进的12-Bit格子气模型用于复杂边界的热声发动机的模拟研究,成功模拟了带共振腔的驻波管中热声振荡演化过程。对热声板叠的长度、热声板叠在共振管中的位置以及共振腔的几何大小对热声振荡振幅的影响进行了数值计算。计算结果显示,当共振腔与细管的宽度比为2.2,板叠位置相对于细管长为0.34时,驻波管中热声振荡振幅达到最大。共振腔尺寸的研究,对于热声发动机性能的的优化设计有指导意义。     

热声热机声场的格子气分析

从格子气自动机演化方程恢复了宏观热声方程,采用D2Q9热格子气模型模拟热声热机系统的压力场、温度场和速度场,获得压力驻波的传播和反射过程。模拟结果显示,在所给模拟条件下压力波具有非线性的特征,变截面附近的流场区域会产生引起非线性耗散的涡流。本文也分析了谐振管几何尺寸及格子气粒子密度对系统频率和压力的影响,验证了热声热机格子气模型的有效性。     

气液耦合振动对热声发动机性能的影响

进行了气液耦合振动驻波型热声发动机定量模拟.重点比较分析了单纯气体振动系统和引入[EMIM][BF_4]室温离子液体作为液体活塞的气液耦合振动系统的运行参数,并考察了液体活塞的质量对热声发动机谐振频率、压力振幅以及板叠热端温度等的影响.     

气体工质对气液热声发动机性能的影响

本文针对一台气液耦合振动热声发动机,以1．5kg的水作为液柱,以氮气、氦气、氩气和二氧化碳分别作为气体工质,在2．0MPa平均工作压力下,实验对比了不同气体工质对谐振频率、压力振幅和板叠热端温度等系统性能参数的影响。实验结果表明,在相同加热功率下,采用氩气的系统获得的压力振幅最大;而在相同板叠热端温度下,以二氧化碳为气...     

非平行板叠驻波型热声发动机热力性能研究

热声发动机板叠两端存在较大的温度梯度,导致沿板叠轴向的热渗透深度出现严重的不均一性,影响到热声转换效应的发挥。本文提出了板叠结构形式与温度梯度相一致的结构设计理念,并构建了非平行板叠结构的驻波型热声发动机数理模型。针对不同板叠锥角热声发动机的热力性能展开了深入研究和对比分析,得出板叠锥角对热声发动机频率、压比、压力振幅和体积流率等热力参数的影响关系。结果表明:与平行板叠结构相比,当选取合适锥角时,渐缩和渐扩式板叠结构均可提高热声系统的性能,在1°和-2.81°时系统的最大声功流分别提高了103.9%和88.8%。研究结果为进一步改善热声热机性能提供理论支撑。     

二维谐振腔中声驻波的格子气仿真

引入带温度的９－Ｂｉｔ正方形格子气自动机模型,利用Ｍｏｎｔｅ Ｃａｒｌｏ方法模拟原并激发平面波,在二维谐振腔中建立了声驻波场。该模型能够动态地反映声波的建立和演化过程,为进上步模拟分析热声效应等物理过程提供了可视化的有力工具。     

热声发动机的CFD数值模拟

采用计算流体动力学(CFD)方法,对高频驻波热声发动机和热声斯特林发动机实验系统分别进行了二维和三维数值模拟。计算模型具有与实验系统相同的几何结构、尺寸和运行工况。对计算模型的有效性进行了研究,表明实现有限换热条件的板叠实物模型适合驻波热声发动机的模拟,而实现局域热平衡的多孔介质模型适合热声斯特林发动机的模拟。计算结果成功观测到了非线性的自激振荡演化过程,捕捉到了两种发动机的不同非线性现象。计算结果分别给出了两种热声发动机内部的声场分布特性和复杂流场。计算结果与实验结果的对比验证了CFD方法对高频驻波热声发动机和热声斯特林发动机模拟的有效性。     

基于场协同理论的热声回热器数值研究

热声回热器是热声热机的重要部件。基于Rayleigh准则,提出回热器内流固之间的对流换热强度是影响热声热机整体性能的重要因素。利用改进的数值模型,模拟了平行板叠内回热器的速度与温度分布特性,并分析了板叠内部对流换热及整机性能之间的对应关系。此外,基于强化对流传热的场协同理论,提出了4种新型结构的异型回热器,并分别对其换热性能与热声转换性能进行了对比分析研究:表明采用混合型回热器的热声热机具有更优越的工作性能,输出声功的压力振幅较普通结构回热器可提高2.8%。研究结果验证了热声回热器内部对流换热强度与热声热机性能呈正相关性,通过改良回热器结构可有效提高热声热机的热声转换性能。     

热声制冷机的一种非线性模型研究

为研究热声制冷机内部的非线性过程,发展了一种可考虑管道截面积变化的时域准一维非线性热声模型,其主控方程由可压流基本控制方程经截面平均的数学处理推导得出,数值求解采用具有频散保持特性的高精度计算格式。采用该模型分别针对活塞、扬声器和热声发动机这三种不同驱动源,将驱动源和热声制冷机进行整体求解,模拟了热声制冷板叠两端温度差在气体微团吸放热的循环过程中逐渐增大的整个过程,预测了谐振管内部驻波的非线性畸变。进而研究了平均工作压力、板叠材料、板叠位置以及扬声器形状等参数的选取对于热声制冷机制冷效果的影响。     

Modeling of pedestrian evacuation under fire emergency based on an extended heterogeneous lattice gas model

An extended heterogeneous lattice gas (E-HLG) model is developed by introducing an altitude factor into the heterogeneous lattice gas (HLG) model. The altitude factor is used to describe the position height of lattice sites. Evacuation features from a terrace classroom are investigated through simulations using both the model and experiments. To study evacuation processes under fire emergency, an agent-based fire and pedestrian interaction (FPI) model is proposed. It is supposed that the possible moving directions of a pedestrian depend on the environmental temperature field, which is simulated by the software FDS. The walking speed reduction due to the visibility worsening in the FPI model is described by a multi-grid method. It is found that simulation results based on the extended HLG model are in good agreement with the experiments. The altitude factor plays a guidance role to the evacuation, and the fire notably delays the evacuation due to both the harmfulness of the high temperature field and the change of evacuation routes which results in frequent local jamming and clogging.     

二维卡门涡街的格子Boltzmann仿真

格子气自动机和格子Boltzmann方法的迅速发展提供了一类求解流体力学问题的新的方法。本文中，我们介绍了Boltzmann方法，解决了格子气方法中的缺点，通过选择适当平衡分布及其参数，导出了Navier－Stokers方程，并得到了声速和粘性系数。最后在微机上模拟了在无限长平板流动问题及绕单分离板的流动问题，得到了卡门涡街。结果表该模型有格子气方法及其它的数值方法所没有的优点，计算更精确、更直观、更有效。     

Condensation in a steady-flow thermoacoustic refrigerator

Condensation may occur in an open-flow thermoacoustic cooler with stack temperatures below the saturation temperature of the flowing gas. In the experimental device described here the flowing gas, which is also the acoustic medium, is humid air, so the device acts as a flow-through dehumidifier. The humid air stream flows through an acoustic resonator. Sound energy generated by electrodynamic drivers produces a high-amplitude standing wave inside of the resonator, which causes cooling on a thermoacoustic stack. Condensation of water occurs as the humid air passes through the stack and is cooled below its dew point, with the condensate appearing on the walls of the stack. The dry, cool air passes out of the resonator, while the condensate is wicked away from the end of the stack. Thermoacoustic heat pumping is strongly affected by the form of the condensate inside of the stack, whether condensed mostly on the stack plates, or largely in the form of droplets in the gas stream. Two simple models of the effect of the condensate are matched to a measured stack temperature profile; the results suggest that the thermoacoustic effect of droplets inside the stack is small.     

小体积比两相分离早期过程的三维格子气模型研究

采用Monte Carlo模拟方法研究了小体积比三维格子气模型中的相分离过程, 比较了sc, fcc, bcc 等3种晶格类型和T/T_c=0.45–0.85等 5个相对温度的系统演化行为, 计算了系统的结构因子函数, 发现结构因子在相分离早期不满足标度关系, 生长指数等于1/6, 小于经典Lifshitz-Slyozov理论的值. 关键词： 格子气模型 相分离过程 Monte Carlo模拟 生长律     

Influence of stack geometry and resonator length on the performance of thermoacoustic engine

Thermoacoustic engines convert heat energy into high amplitude sound waves, which is used to drive thermoacoustic refrigerator or pulse tube cryocoolers by replacing the mechanical pistons such as compressors. The increasing interest in thermoacoustic technology is of its potentiality of no exotic materials, low cost and high reliability compared to vapor compression refrigeration systems. The experimental setup has been built based on the linear thermoacoustic model and some simple design parameters. The engines produce acoustic energy at the temperature difference of 325–450 K imposed along the stack of the system. This work illustrates the influence of stack parameters such as plate thickness (PT) and plate spacing (PS) with resonator length on the performance of thermoacoustic engine, which are measured in terms of onset temperature difference, resonance frequency and pressure amplitude using air as a working fluid. The results obtained from the experiments are in good agreement with the theoretical results from DeltaEc.     

An open-air infrasonic thermoacoustic engine

A low-frequency open-air thermoacoustic engine in a Helmholtz resonator has been constructed. Tests indicate that the system resonates in the Helmholtz mode for modest thermoacoustic stack temperature differences using stacks of varying type and pore size located within the neck of the Helmholtz resonator. The maximum acoustic pressure radiated from the open end of the resonator corresponds to 81 dB-SPL ref 20 μPa at a stack temperature difference of 185 K and an input electric power of 276 W. The system is well characterized by a numerical model of a representative stack.