| Budget Amount *help |
¥7,400,000 (Direct Cost: ¥7,400,000)
Fiscal Year 2000: ¥2,700,000 (Direct Cost: ¥2,700,000)
Fiscal Year 1999: ¥4,700,000 (Direct Cost: ¥4,700,000)
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| Research Abstract |
Acoustic standing wave induced in a tube is one of well-known and fundamental physical phenomena. Physical properties, such as pressure and velocity distributions, mode of oscillation, and so on, observed in acoustic standing waves are well evaluated by linear acoustic theory. On the other hand, finite amplitude standing waves induced in a tube accompanying nonlinear phenomena still have unsolved problems. In recent engineering applications of finite amplitude standing waves for new technology in fluid or thermofluid engineerings such as thermacoustic refrigerator and acoustic compressor, realization of large amplitude shockless-standing wave is required to avoid acoustic saturation, which causes the suppression of thermoacoustic effect or increasing ratio of pressure amplitude. It has been reported the finite amplitude shockless standing wave can be realized in a tube with cross-sectional area change along the axis. The acoustic compressor composed by a gas-filled closed tube and a dr
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iving piston will be design with this concept. However, the fundamental characteristics of the finite amplitude standing wave in a gas-filled closed tube driven by a piston with area change has not been analyzed in detail. In this research, the physical properties of the finite amplitude wave motion induced in different shaped tubes have been evaluated by using linear acoustic theory, numerical simulation and experiments. The numerical results on resonant frequency and oscillation modes induced in an exponentially area change tube agree well with the predictions based on linear theory. The limit of area contraction ratio to realize the shockless standing wave and the effect of area contraction to obtain high compression ratio for different shaped tubes are clarified by the numerical calculation. The results in the limited condition are verified by the experiments.
As another application, coupling effect of acoustic standing wave to thermal convection has been investigated. The thermal convection generated in a horizontal closed duct, which has rectangular cross-section, at high Rayleigh number is unsteady or turbulent. When the acoustic standing wave is combined with the unsteady thermal convection, the thermal convection is constrained into steady roll type convection characterized with 1/4 wavelength of sound, In this research, the velocity and density field of the coupling convection have been measured by using PIV method and digital laser speckle photography. The results obtained show the acoustic standing wave is playing the role of control of unsteadiness in thermal convection.
The above-mentioned results give us useful knowledge for applications of acoustic standing waves to new fluid or thermofluid technology. Less
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