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在热声发动机系统中,谐振管用来调节系统的超振频率.通常的四分之一波长谐振管由一段谐振管后面连接一个比较大的气体容积构成,与二分之一波长谐振管相比,在相同的起振频率下前者可以有相对短的管长.锥形谐振管除了调节频率外,还可以提高热声发动机输出压力波的压比.本文通过数值计算软件Fluent6.0中的K-ε湍流模型模拟了不同长度、不同的进出口直径的一系列锥形谐振管,得出了近似四分之一波长锥形谐振管的共振频率与其长度、锥度之间的关系,并初步与实验进行了对照. 相似文献
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An ignition time model is developed to model super knock in a compression engine. The model assumes that thermoacoustic interaction is the primary mechanism for the onset of super knock. By ignoring diffusive effects, a simple transport equation for the time to ignition of a fluid particle is derived. The significantly reduced cost of the chemistry model allows for complex hydrocarbon fuels to be simulated. Additionally, a zonal model for the secondary ignition of a charge due to the action of an expanding flame is developed. The flame compresses the unburned gas, causing the temperature and pressure to rise, which yields a pre-ignition in the unburned gas before the charge is engulfed by the flame. It is shown that the ignition time model compares well to the detailed chemical model with less than 1% difference in the prediction of ignition delay. Using this ignition time model, a multi-dimensional simulation of super knock in a rapid compression machine corresponding to the configuration of Wang et al. [1] is performed. It is found that interaction of the shock with the flame and the side wall of the cylinder significantly enhances the strength of the shock, and the in-cylinder pressure exceeds 300 bar. From the pressure rise predicted by the simulation, it is concluded that simulated ignition is a super knock event. Since the ignition time model excludes diffusive effects on the chemistry, it is proposed that acoustic resonance of the cylinder is the primary driver in the development of super knock for the configuration under examination and that inhomogeneous ignition due to transient flame compression could be a key mechanism for super knock. 相似文献
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热力学循环的实质是一种非等熵的循环 ,热声热机和斯特林热机振荡现象在满足热力学循环一般规律的同时 ,而各有其特殊性 ,故其各自的振荡本质是有差异的 ,用于描述两者的网络模型也必然有差异。 相似文献
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In thermoacoustic travelling-wave engines and other Stirling cycle devices, good performance depends on the material of a regenerator being in intimate contact with the gas inside it, so that each particle of gas oscillates in temperature following the adjacent material as it is acoustically displaced. This requires that the passages are small enough for temperature waves to penetrate across the gas path with the frequencies of interest. One type of ‘regenerator’ that is commonly used for this purpose is composed of multiple layers of woven stainless steel mesh, laid on top of one another in random registration. Associated with the thermal penetration is a viscous loss of pressure and this must be quantified if efficient engines are to be designed.In the literature, reliance has been placed on the correlation of steady-flow loss data for these meshes, but for the coarser ones operating at frequencies greater than 28 Hz, the assumption of quasi steady-flow is dubious and direct acoustic measurements must be made. This paper reports acoustic pressure loss data for meshes with 34 and 75 wires per inch taken in two configurations of impedance tube, and finds that the dependence on velocity is the same as in steady-flow, but that there is indeed some enhancement of loss for frequencies above 40 Hz. (Separation of the mesh layers is probably responsible for the anomalously low loss coefficients that were recorded in one set of data.) It is shown that the acoustic pressure losses can be correlated in terms that give the acoustic impedance more directly than the friction factor correlations. 相似文献
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