Study On Numerical Simulation Of The Start-oscillation Process Of Standing Wave Engine

The thermoacoustic engine is a new type of thermodynamic device with absolutely no moving mechanical parts.It uses inert gas as the working medium and relies on low-grade heat source to heat the gas medium in the system to generate acoustic spontaneous oscillating phenomenon in order to achieve the conversion of heat energy to acoustic energy.This new "green" technology can not only effectively solve the energy problem caused by the shortage of fossil fuels,but also fundamentally avoid the energy loss caused by friction and oscillation during the movement of mechanical components,so it has a wide range of applications in power generation,refrigeration,liquefied natural gas and other fields.Therefore,the thermoacoustic engine is widely concerned by researchers at home and abroad.The start-oscillation process of standing wave engine is a complicated process involving the conversion of thermal energy and acoustic energy and the nonlinear spontaneous oscillation,the theoretical study of this process needs to be further explored,and it is very important to research the start-oscillation process of the thermoacoustic engine to improve the thermoacoustic conversion efficiency of the engine.Thermoacoustic engine's internal flow,heat transfer and thermal processes are highly coupled,and computational fluid dynamics(CFD)is widely used in the flow and heat transfer problems.On this basis,this paper uses CFD method to simulate the start-oscillation process of the standing wave engine,the two-dimensional geometric model of standing wave engine is established by comparing with the physical model of engine.In order to make the internal area of each component of standing wave engine better communicate with each other,the unstructured grid which can realize the smooth transition of the grid is used to discretize the area.Under the condition of using 1.0MPa nitrogen as the working medium,the start-oscillation process of standing wave engine is simulated by fixing heating,and the complete spontaneous oscillation phenomenon is successfully observed.This can further enhance the thermoacoustic researchers' understanding of the start-oscillation process of standing wave engine.Then,the Fourier analysis of the simulation results shows that there is a phenomenon of second resonance during stable oscillation.Finally,this paper explores not only the relation between the start-oscillating time and heating as well as that between the saturation pressure and heating,but also the relationship between the fundamental frequency and the length of the resonance tube.These conclusions are of guiding significance for the optimization and improvement of the standing wave engine.