Development, Trial Manufacture an Evaluation of Acoustic Compressor

封闭管内有限振幅波动是近年来先进技术应用的一个经典而有趣的研究领域。当密闭管内的气柱一端由活塞以谐振频率驱动时，管内会产生较大的驻波。驻波的模态、压力波形及其闭端振幅与管形的几何形状密切相关。在圆柱管中，由于波前变陡产生的传播冲击波的非线性效应，使得波形的幅值受到限制。声饱和很快就会到来，因为在现有频率模式下产生驻波的能量被耗散到更高的谐波上，而不是增加压力波形的幅度。另一方面，在变截面积管中，可以产生大振幅驻波，激波随波的运动而消失。这种大幅度的压力波动在声学压缩机的研制中具有实际应用价值，可构成无油气体压缩系统。封闭管内的大振幅驻波还引起了沿管轴线的非零平均压力分布、每1/4波长段的稳定循环流动以及压力波动节点的冷却和回路加热的热声效应。声流与不稳定对流的耦合不仅使其转化为具有以声波波长为特征的细胞结构的稳定对流，而且使对流速度增大。气柱振荡引起的热声效应可应用于热声发动机和制冷机的设计。管形的几何形状是圆锥形、指数或半余弦函数的横截面积向封闭端收缩。圆柱形管作为基准管。每根管子的长度是一样的。所有的管的面积都与管的轴对称。管内有限振幅波动是由各管大端活塞的正弦振荡引起的。利用流体动力学的基本方程推导出了线性和非线性理论。利用线性理论，可以计算出不同形状、不同面积收缩比的管的谐振频率。并可用于热声发动机和制冷机设计中，对烟囱板放置在管内所需的节点位置进行估计。基于Chester理论的非线性理论表明，改变管的形状可以减小封闭圆柱管中波形的不连续。非线性计算结果与前人的研究结果吻合较好。采用时间上保持二阶精度、空间上保持四阶精度的有限差分MacCormack格式对密闭管内波动进行了数值模拟。考虑了粘滞耗散和摩擦耗散，求解了一维流体动力学方程。通过数值模拟研究了激波出现的截面积收缩比极限、管长和气体性质的影响。数值结果表明，通过改变管的截面积，可以得到无冲击的高振幅压力波形。建立了实验装置，研究了不同管形下的波动特性。采用锥形收缩管、指数收缩管和半余弦面积收缩管，比较了不同形状收缩管的硬化、迟滞和频移。对不同的活塞加速度进行了实验，并与数值模拟结果进行了比较。本文从理论、数值和实验三个方面对密闭换热管内有限振幅驻波进行了研究。实验结果与数值和理论结果吻合较好。研制了高振幅无冲击压力波形和高压缩比的密闭换管。并对不同气体条件下不同形状管的压缩机模式运行特性进行了研究。结果表明，管形的几何形状是确定无激波高幅值压力波形和获得稳定谐振频率的最重要因素。半余弦型面积变换管是本研究中设计声学压气机的最佳管型。少

Finite amplitude wave motion in closed tubes are classic but interesting research field for the applications in recent advanced technology. When the gas column in a closed tube is driven by a piston at one end at the resonant frequency, large amplitude standing wave is induced in the tube. The mode of the standing wave, the pressure waveform and its amplitude at the closed end strongly depend on the geometry of the tube shape. In the case of cylindrical tube, the amplitude of the waveform is restricted due to the nonlinear effect in propagating shock-wave generation by the steepenig of wave front. Acoustic saturation comes quickly because the energy supplied to generate standing wave at exiting frequency mode is dissipated to higher harmonics instead of increasing the amplitude of the pressure waveform. On the other hand, in varying cross-sectional area tube, a large amplitude standing wave can be achieved and shock waves disappear with the wave motion. This large amplitude pressure fl … More uctuation has a practical application in the development of acoustic compressor which can consist an oil-less compression system of gases. The large amplitude standing wave in closed tube also induces non zero mean pressure distribution along the tube axis, steady circulating streaming at every 1/4 wave length section, and thermoacoustic effect of cooling at the node of pressure fluctuation and heating at the loop. The coupling of acoustic streaming with unstable convection not only transforms it into stable convection with cellular structure characterized by the wavelength of the sound wave but also increases the velocity of the convection current. Thermoacoustic effect induced by the air column oscillation can be applied to design thermoacoustic engine and refrigerator.The geometry of the tube shape is conical, exponential or half cosine function cross-sectional area contraction towards the closed end. The cylindrical tube is used as reference tube. The length of each tube is same. All the tubes area symmetric with regards to axis of the tube. The finite amplitude wave motion is induced in tube by sinusoidal oscillation of piston at big end of each tube. Linear and nonlinear theories have been derived by using the basic fluid dynamics equation. By the linear theory, the resonant frequency can be evaluated for different shaped tubes with different area contraction ratios. And it can be used to estimate the node position which is necessary to place the stack plate in tubes to design thermoacoustic engine and refrigerator. The nonlinear theory based on Chester' theory reveals that changing the shape of the tube can reduce the discontinuity of the waveform appeared in closed cylindrical tube. The result obtained by the nonlinear calculation agrees well with previous investigation.Finite difference MacCormack scheme keeping accuracy with second order in time and fourth order in space was used for numerical simulation of wave motion in closed tube. One-dimensional fluid dynamic equations are solved taking viscous and frictional dissipation into considerations. The limit of cross-sectional area contraction ratio to which shock wave appears, the effect of tube lengths, and effect of gas properties is investigated by numerical simulation. Numerical result revealed the possibility of getting shockless high amplitude pressure waveform by changing cross-sectional area of the tube.An experimental setup was made to investigate the characteristics of wave motion in different tube geometries. Conical, exponential and half cosine area contraction tube was used to compare the hardening, hysteresis and frequency shift in each tube geometries. Experiments were conducted for different piston acceleration and results are compared with the results obtained by numerical simulation.The finite amplitude standing wave in closed area change tubes was studied theoretically, numerically and by experiment. Experimental result agrees well with the numerical and theoretical result. The high amplitude shockless pressure waveform as well as high compression ratio in closed area change tube was developed. And the characteristic of the compressor mode operation for each shaped tube has been investigated for different gases.As the results, it has been revealed that the geometry of the tube shape is the most important factor in determining shock free high amplitude pressure waveform and obtaining the stability of the resonant frequency. And the half cosine shaped area change tube is the best tube shape to design acoustic compressor in this investigation. Less