Experimental investigation on large amplitude standing wave induced in closed tubes with varying cross section

概要

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When a gas-filled closed tube is driven near the resonant frequency of the gas-column, large amplitude standing wave is induced in the tube. The use of large amplitude standing wave in practical field is based on the exploitation of high amplitude pressure fluctuation together with the associated phenomena like acoustic streaming, thermoacoustic effect and mean pressure distribution. It is already known that shock wave appears in cylindrical tube and thereby the wave motion is limited in the peak pressure that can be generated. In shaped tubes, it is possible to avoid the problem of shock formation and as a result, large amplitude standing wave can be achieved. And also the mode of standing wave induced in shaped tubes depends on the tube geometry. For practical application of large amplitude standing wave, the selection of optimum tube shape must be required. In this report, experimental results are described for three types of tube geometry, such as conical, exponential and half cosine. HFC134a was selected as the working gas for the reason that the effects of tube geometry in the wide range of pressure amplitude can be investigated than air. The frequency responses and pressure fluctuation at closed end of each tube were monitored. The result revealed that the half cosine geometry is suitable in the case of design of the acoustic compressor.
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