Analysis of Finite Amplitude Wave Motion in Acoustic Compressor using a Duct with Varying Cross-Section.

首先，对数值分析结果进行了描述。针对活塞正弦振动驱动的声压气机密闭管内空气柱的有限幅值波动，采用了时间上二阶精度、空间上四阶精度的显式Mac-Cormack方法进行数值分析，并在截面积缩减比1 ~ 100范围内进行了详细分析。特别是考虑到声压气机在排气和进气过程中的实际运行情况，建立了基于气门运行状态的边界条件。壁面摩擦项不仅考虑了基于瞬时流速的定常摩擦项，而且考虑了非定常摩擦项。从分析结果中，澄清了以下事实。虽然管闭端压缩比随着截面压缩比的增大而增大，但当截面压缩比大于16时，出现了传播性激波，并抑制了压缩比随活塞幅值增大而增大的速率。在较宽的活塞振幅范围内，截面减量比增大，压缩比也增大，得到无冲击共振。但截面压缩比在50以上效果不显著。在数值分析中引入了基于阀门实际运动的边界条件，出现了波动不稳定现象。结果表明，需要进一步改进边界条件。然后，给出了实验验证结果。本实验采用了横截面呈指数缩小的轴对称声管（横截面缩小比为100）和横截面为等横截面的管。在模具谐振点附近，利用电磁加速器驱动活塞对管内气柱进行激励。并且测量了波的运动。通过提高整个系统的刚度，尝试提高测量精度。此外，高精度位移计的引入提高了活塞位移测量的精度。计算结果表明，等截面管内压力波动的幅值和封闭端压力波动的波形与计算结果吻合较好。然而，管的实验结果与计算结果不一致，这表明，在大截面折减比情况下，数值分析需要改进。少

First, the results of numerical analysis are described. On finite amplitude wave motion of the air column in a closed tube with cross sectional area contraction for the acoustic compressor which is driven by a piston oscillating sinusoidally, the numerical analysis based on explicit Mac-Cormack method with second order accuracy in time and fourth order accuracy in space was applied, and the detailed analysis within cross section reduction ratio 1 - 100 was carried out. Especially, boundary condition based on valve operating condition considering the acoustic compressor real operation in exhaust and intake processes was newly set in this analysis. And also in the wall friction term, not only steady term based on the instantaneous flow velocity but unsteady friction term was considered. From the analytical result, following fact clarified. Though the compression ratio at the closed end of the tube increases with the increase in the cross section reduction ratio, under cross section reduc … More tion ratio of 16, the propagating shock wave is appeared, and it suppresses the increasing rate in compression ratio with increase of the piston amplitude. The shockless resonance is obtained in the wide range of the piston amplitude, when the cross section reduction ratio increases, and the compression ratio also increases. But the effect of the cross section reduction ratio is not remarkable over 50. In the numerical analysis introduced boundary condition based on actual motion of valves, the instability of wave phenomenon appeared. It shows that improvement of further boundary condition is required.Next, the experimental verification result is described. In this experiment, an axisymmetric acoustic tube (cross section reduction ratio 100) in which cross section is exponentially reduced and a tube in which cross section is constant cross section were used. The air column in these tubes was excited using the piston driven by the electromagnetic accelerator in die resonance point vicinity. And the wave motions were measured. By raising the rigidity of the whole system, the improvement in the measurement accuracy was attempted it. In addition, the accuracy of the piston displacement measurement was improved by the introduction of high-precise displacement gage. The results obtained show that the pressure fluctuation in the tube with constant cross section was closely coincident with calculated result in the amplitude and in the wave form at the closed end of the tube. However, the experimental results for the tube with cross section reduction was not coincident with the calculated results, and it shows that the improvement of numerical analysis in the case with large reduction ratio of cross section is required. Less