It is necessary to study finite-amplitude standing wave phenomena, which are induced in a closed duct, in detail for its recent application in engineering. Nonlinear phenomena caused by the finite amplitude standing wave strongly depend on the interior shape of the duct. This paper describes fundamental characteristics of finite amplitude standing wave generated by the vibration of a piston in closed acoustic ducts with cross-sectional area changing along its axis. The ducts used are axisymmetric exponential and conical shaped. Constant area duct is used to compare the results obtained in area-change ducts. One-dimensional numerical simulation is conducted using finite difference MacCormack scheme keeping accuracy with second order in time and fourth order in space. Experiments have been done in constant, exponential and conical duct with area contraction ratio 100. The general characteristics of the wave motion were investigated for two types of gases named air and refrigerant. Simulations were performed taking viscous dissipation term in the duct into consideration. Calculated results show the effects of the cross-sectional area contraction ratio and the driving piston amplitude on the wave motion in the ducts, such as resonant frequency, pressure waveform, amplitude of pressure fluctuation, and compression ratio. It is seen that the shock-less standing wave can be realized in exponential and conical ducts and large amplitude of pressure as well as high compression ratio is possible to obtain in a duct with cross-sectional area change. Results obtained by numerical simulations have a good agreement with experiment and linear acoustics theory. This gives new insight into consideration of duct shape in designing acoustic compressor.
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