Development, Trial Manufacture an Evaluation of Acoustic Compressor

封闭管道中的有限振幅波动问题是近年来在高新技术领域中应用的一个经典而又有趣的研究领域。当一端的活塞以共振频率驱动封闭管内的气柱时，在管内会产生大振幅的驻波。驻波的模式、压力波形及其在封闭端处的振幅强烈地取决于管形状的几何形状。在圆柱管的情况下，由于波前陡化产生的传播激波的非线性效应，波形的振幅受到限制。声饱和很快到来，因为供应以在退出频率模式下产生驻波的能量被耗散到更高的谐波，而不是增加压力波形的振幅。另一方面，在变截面管中，可以获得大振幅的驻波，并且激波随着波动而消失。这种大振幅压力FL ...更多信息 脉动理论在声学压缩机的研制中有实际应用，可构成气体的无油压缩系统。大振幅驻波在封闭管中还引起沿管轴沿着非零平均压力分布，在每1/4波长段产生稳定的循环流动，以及在压力波动节点处产生冷却和在回路处产生加热的热声效应。声流与不稳定对流的耦合不仅将其转化为具有以声波波长为特征的蜂窝结构的稳定对流，而且还增加了对流的速度。气柱振荡引起的热声效应可用于热声发动机和制冷机的设计，其管形可为截面积向封闭端收缩的圆锥形、指数形或半余弦函数形。圆柱形管用作参考管。每根管子的长度都是一样的。所有管关于管的轴线区域对称。通过活塞在各管大端的正弦振动，在管内诱导出有限振幅的波动。从流体动力学基本方程出发，推导了线性和非线性理论。利用线性理论，可以计算出不同截面收缩率的不同形状管的共振频率。该方法可用于热声发动机和制冷机设计中确定热声管中叠层板的节点位置。以Chester理论为基础的非线性理论揭示了改变管的形状可以减小封闭圆柱管中出现的波形不连续性。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格式对封闭管内的波动进行了数值模拟。考虑粘性耗散和摩擦耗散，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收缩比的极限、管长的影响以及气体性质的影响。数值计算结果揭示了通过改变管道截面积获得无激波高幅值压力波形的可能性。采用圆锥形、指数形和半余弦面积收缩管，比较了各种几何形状收缩管的硬化、迟滞和频移。在不同活塞加速度下进行了实验研究，并与数值模拟结果进行了比较，对封闭面积变化管内的有限振幅驻波进行了理论、数值和实验研究。实验结果与数值计算和理论分析结果吻合较好。开发了封闭变截面管内高压缩比的高振幅无激波压力波形。研究了不同形状管对不同气体的压气机模式工作特性，结果表明，管的几何形状是决定无激波高振幅压力波形和获得谐振频率稳定性的最重要因素。半余弦形变截面管是本研究中设计声压缩机的最佳管形。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