基于气体动理学方法的热声热机非线性效应模拟与装置优化研究

In the thermoacoustic engine, there are many nonlinear effects, which are closely related with the energy transfer and transport and directly effect the efficiency of the thermoacoustic engine. However,there is few effective quantitative analysis method for these large amplitude and strongly nonlinear effects. Therefore, it is important for the improvement of the efficientcy of the energy transfer and transport to investigate the numerical simulation method of the nonlinear thermoacoustic engine and to optimize the structure and the working condition of the thermoacoustic engine. For this purpose, this project will develop the nonlinear numerical simulation method based on the gas-kinetic scheme for the large amplitude and strongly nonlinear thermoacoustic problems, promote the understanding of the energy transfer and transport mechanism in the thermoacoustic engine, and optimize the design and working condition of the thermoacoustic engine aiming at improving the efficiency. The contents of the project are listed as follows: modeling the thermoacoustic engine equipped with variable cross-section resonators; presenting the simulation methods based on the multidimensional gas-kinetic BGK scheme for nonlinear thermoacoustic; simulating the nonlinear effects in the different geometric dimension thermoacoustic engines and verifying the simulation results by experiment; and optimizing the structure and the working condition of the thermoacoustic engine based on the nonlinear numerical simulation to improve the efficiency of the energy tranfer and transport. Some novel nonlinear quantitative analysis and design methods and new data supports are provided for the research of thermoacoustic and the design of the related devices, which will enrich the contents of the nonlinear thermoacoustics and promote the development and industrialization of the thermoacoustic engine.

热声热机中存在大量非线性效应，能量的转换和输运效率与这些非线性效应有密切关系，对于这些非线性效应特别是大振幅、强非线性效应目前还缺乏有效的定量分析方法。因此，开展热声热机非线性数值模拟分析方法研究，优化热声热机结构与工况，对提高热声热机能量转换效率有着重要意义。为此，本项目针对热声装置中大振幅、强非线性热声问题，发展基于气体动理学方法的热声非线性数值模拟方法，深化热声能量转换机理的认识，以提高转换效率为目标优化热声热机的设计和工况。具体研究内容包括：建立具有变截面谐振管的热声热机的物理数学模型；基于气体动理学BGK方法的热声非线性数值模拟方法；不同几何尺寸热声热机中热声非线性数值模拟分析与实验；基于数值模拟的热声热机结构优化与工况分析，提高能量转换和输运效率。为热声研究和装置设计提供新的非线性定量分析和设计方法以及数据支持，丰富非线性热声理论内容，促进热声热机的开发与产业化。

热声热机具有可以利用低品质热能等许多优点，具有广泛应用前景。但由于对热声热机内交变流动的理论缺乏深度了解，对其中能量转换物理机制和非线性耗散的认识还不够深入，没有成熟的定量分析方法，导致不恰当的设计，使得热声热机效率还不高，因而还未得到广泛的商业推广。. 本项目主要研究内容、重要结果、关键数据：(1) 构造了一个新的热声计算方法，通过与DeltaEC比较，该方法是有效和准确的。该方法能与其它优化方法耦合实现对热声热机的优化; (2) 基于该方法，优化了热声制冷机板叠部分，优化结果显示当相对于波长的板叠长度和位置分别约为0.24和0.21，板叠间距约为2.9个热渗透深度，孔隙率约0.94时制冷量可以达到最大；同时以性能指标和制冷量为多目标的优化结果为设计者提供了更多设计选择; (3) 在考虑滑移边界和温度跳跃边界条件情况下，建立了微型热声热机的弱线性模型，为微型热声热机的设计提供分析工具; (4) 建立了谐振管的简单理论模型，以此设计了一个简单、有效、普适性好的热声谐振管谐振频率计算方法; (5)提出了一个新的评价热声谐振管性能的性能指标，该性能指标只与谐振管形状有关，并给出了该性能指标的简单计算方法。基于该性能指标，计算了锥形、半余弦形、3/4余弦形、锥-号筒形等谐振管的最优形状参数。并得到了锥形-号筒型谐振管是几类常见谐振管中性能最好的结论。为谐振管的优化提供了新的途径; (6) 构造了变截面热声谐振管非线性高维分析的气体动理学模型; (7)通过模拟不同谐振管内非线性振动和非线性声流场，分析了激波、高次谐波、频率漂移、非线性振幅饱和、声流、涡流、谐波耦合等耗散现象的声流场特征量，探讨了耗散过程中声流场特征量的变化规律，揭示各耗散现象的本质机理，指出形状参数在2.0~2.3之间的指数型谐振管既能抑制激波也能抑制声流。. 本项目的研究结果为复杂热声系统和实用装置的开发提供了新的数值分析方法，同时也为高效的热声热机的设计提供理论依据和数据支持.