|Budget Amount *help
¥3,300,000 (Direct Cost : ¥3,300,000)
Fiscal Year 1998 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 1997 : ¥2,400,000 (Direct Cost : ¥2,400,000)
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
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.