锥型热声谐振管内非线性声场的数值模拟研究

从声学角度出发,考虑粘性耗散、非线性效应及管型结构变化的影响,利用伽辽金法,对锥型热声谐振管内的一维声场进行了数值模拟研究,对谐振管结构参数对声场的影响进行了分析,给出了锥型管内压比随谐振管结构参数变化的规律,通过与圆柱型直管的比较,揭示了锥型管在抑制谐波及提高压比等方面的优越性。     

三级行波热声发动机的声场特性

设计并搭建了一台三级行波热声发动机,并基于线性热声理论和实验研究分析了该热声发动机的声场特性。结果表明:理论计算中各级加热功率相同时,发动机声场对称;而实验中加热功率相同时声场存在不一致性,需要输入特定的加热功率来控制三级加热温度基本相同,从而保证三级声场基本对称,此时相邻两级对应位置的压力相位差在120°±10°范围内;随着充气压力和加热温度的升高,系统工作频率略有升高,变化不显著,系统压力振幅和压比则增大明显。以氮气和氦气为工质时,工作频率分别在20 Hz和55 Hz左右;实验中压比分别达到了1.28和1.18。     

热声谐振管的实验研究

本文主要介绍作者热声谐振管研制方面的工作，作者成功地研制了热声谐振实验装置系统。     

热声谐振管品质因数的实验研究

回热器中填充了玻璃丝绵,在声驱动的热声谐振管中发生共振,通过测量谐振频率,分析热声谐振管的频率特性,辨识谐振管的品质因数,其测量结果能与理论计算值较好的吻合。实验证实,品质因数是评价热声谐振管工作性能的重要参数。     

指数型热声谐振管的固有频率

采用计算流体力学软件Fluent模拟研究了11种不同形状参数的指数型热声谐振管内二维非线性声场特性,分析了驱动频率和驱动强度对管内声压演化过程及固有频率的影响,并探索了指数管的固有频率与理论计算谐频之间的关系.研究发现:当驱动频率偏离谐振管固有频率时,管内将出现明显的\     

近临界区CO_2对热声谐振管性能的影响分析

谐振管是热声热机的主要部件之一,减小声功在谐振管中的耗散对改善热声热机输出特性具有积极意义。由于近临界区流体的热物性具有特殊性,用其作为工质时将会对谐振管内的声功损耗产生重要影响。本文对声功在以近临界区CO_2为工质的谐振管中的损耗情况进行了计算和分析。结果显示,在本文的计算条件下,相较于压力较低的CO_2,采用近临界区CO_2作为工质可降低谐振管内的声功损耗,并在工作压力略低于临界压力时,谐振管内的声功损耗可达到最小值.此外,在保持谐振频率不变的情况下,采用近临界区CO_2作为工质可一定程度上缩短谐振管的长度。     

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.     

热声发动机热缓冲管损失的实验研究

热缓冲管是热声发动机的关键部件之一,位于高温换热器和次室温换热器之间,理想情况下可避免在高温换热器附近往复运动的气体接触室温环境,造成热量损失。不过由于换热器流道的特殊结构,使热缓冲管两端会产生射流等现象,带来流动紊乱、热量损失等问题。本文设计并搭建了研究热缓冲管损失的实验平台,主要考查在热缓冲管两端分别添加不同层流化丝网对系统性能的影响。实验结果表明,未添加层流化丝网会使热量损失急剧增大,热声效率大幅下降;而过多添加层流化丝网会使阻力损失增大,同样降低热声效率;当两端分别添加3片层流化丝网时,所需加热量最少,热声转换效率最高。     

谐振管中混合工质的热声分离效应

本文在可压缩SIMPLE算法的基础上,基于先求解二维热声谐振腔内的速度场和温度场,然后利用求出的速度和温度值求解组分浓度场的思路,对混合工质的热声分离现象进行了数值研究。研究结果表明:在热声效应和热扩散效应共同作用下,声波能够将混合物中的两种气体分别泵向谐振腔的压力腹点和节点,使得混合气体在声波传播方向上逐渐分离。另外,通过考察5种不同管径下谐振管内径向浓度的变化规律,详细研究了浓度边界层在径向上的影响范围以及不同管径下的分离效率,并提出最佳管径应为16倍浓度渗透深度左右。     

指数型谐振管内非线性声场的模拟研究

采用气体动理学方法模拟研究五种不同驱动强度下,=0的圆直热声谐振管和=2 2的指数型热声谐振管内的非线性声场特征。研究发现:指数型管能抑制激波及声饱和现象,但管内会出现尖峰现象。尖峰处的压力波形发生了畸变;它们是非线性的能量传递与各种耗散的竞争过程中产生的不同形态的波特征;当活塞驱动位移幅值400μm时,指数型管内压力振幅增长速度明显下降。     

Influence of resonator shape on nonlinear acoustic field in a thermoacoustic engine

The influence of the resonator shape on nonlinear acoustic field in a thermoacoustic engine is studied.The resonator of themoacoustic engine is boundary driving by a piston at one end,and the other end of it is rigid closed.A one-dimensional wave equation that accounts for gas dynamic nonlinearities and viscous dissipation in the resonator is established based on the governing equations of viscous hydromechanics.The nonlinear wave equation is solved using approximate Galerkin method.The nonlinear acoustic field in four different types of shaped resonators including hyperbolical,exponential,conical and sinusoidal are obtained and compared with that of a cylindrical resonator.It is found that the amplitude and waveform of the pressure are strongly affected by the resonator shape,the driving amplitude and the oscillation frequency of the piston.Waveform distortion,resonance frequency shift and hysteresis are observed,when the piston oscillation amplitude is large enough.The advantages of shaped resonator for thermoacoustic engine lie in inhibition of higher order harmonics and improvement of pressure ratio,etc.     

Influence of resonance tube geometry shape on performance of thermoacoustic engine

Based on the linear thermoacoustics, a symmetrical standing-wave thermoacoustic engine is simulated with a cylindrical tube and a tapered one as the resonance tube, respectively. The experiments with both cylindrical and tapered tubes are carried out. The suppression of nonlinear effects due to tapered tube as the resonance tube is discussed. Both simulation and experimental results show that the performance of the tapered tube is better than cylindrical one as the resonance tube.     

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.     

热声发动机接入声学放大器的模拟研究

对带声学放大器的驻波型热声发动机进行了数值模拟。得出了系统频率、压比等参数随声学放大器尺寸的变化关系。     

Temporal field dynamics in parametric acoustic resonator

The temporal field dynamics in acoustic resonator at high-frequency spatially uniform modulation of the speed of sound in the resonator material with a time-dependent modulation coefficient is described.     

Fishbone-like instability in a looped-tube thermoacoustic engine

Quasi-periodic bursts of acoustic oscillations were observed during the start-up process in a looped-tube thermoacoustic engine. The acoustic oscillations have a constant frequency of 111 Hz, while the bursts have "quasi-periods" in the order of 14-25 s. The quasi-periodic bursts show a new mode of amplitude growth in this thermoacoustic engine. The envelope of the acoustic oscillations has a fishbone-like shape. The nature of the observed fishbone-like instabilities suggests a strong interaction between the acoustic and temperature field.     

微型热驱动热声热机热端换热器的优化设计

该文基于热声环境,采用厘米级扁管和deltaE数值计算对微型热声换热器进行了优化设计。