| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 93 === Due to the process of fuel ignition and explosion inside a vehicle’s engine, the flow inside the exhaust pipe that connects with the engine is a pulsating high- temperature flow with impulsive waves. The impulsive waves move fast, but the pulsating flow and the process of heat transfer are slow. In this study we numerically investigate the pulsating flow with the effects of heat transfer and wall friction. In order to fast and accurately calculate the pulsating flow, a combined time-scaling method is employed for solving the governing equations of the mass, momentum and energy conservations. A steady exhaust-gas flow under the condition of heat loss without impulsive waves at a fixed engine speed is computed by one dimensionless time variable. The computed steady flow is referred as a basic flow with the temperature and flow velocity information. With the computed basic flow, an unsteady pulsating flow inside the exhaust pipe with an imposed blast wave at the pipe inlet is computed by using another dimensionless time variable.
The high-resolution solver is established by using 5th-order WENO scheme and 4th-order Runge-Kutta method for solving the Euler equations with the source terms of the variation of pipe’s cross-sectional area and the effects of wall friction and heat transfer. We found that the computed results at different engine speeds are compared well with the experimental data at some checking points. Moreover, the time variable normalized by the ratio of the pipe length to the time-average inlet flow velocity is appropriate for fast and accurately acquiring the basic flow, and the time variable normalized by the ratio of the pipe length to the time-average inlet sound speed for efficiently predicting the unsteady flow.
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