عنوان مقاله [English]
Streaming appears in almost all traveling wave thermoacoustic engines and refrigerators. This phenomenon may increase or decrease the efficiency of thermoacoustic devices. It should be emphasized that properly designed streaming may also be used to eliminate the required heat exchanger in the abovementioned devices. However, in most cases, due to the lack of the relevant knowledge, this phenomenon is considered as a non-preferred occurrence and a source of secondary losses. Thermal buffer tube separates the hot and ambient heat exchangers in travelling-wave thermoacoustic engines as well as the cold and ambient heat exchanger in pulse-tube refrigerators. The role of the thermal buffer tube is to pass the acoustic energy while minimizing the heat transport due to the boundary-layer entropy flow, heat conduction through the gas and the tube walls, radiation, and mass streaming. The latter is caused by finite-amplitude acoustic oscillations and can transport significant amount of heat between heat exchangers. The heat transport depends on temperatures at the ends of the thermal buffer tube. Acoustic motion of gas parcels between nearly isothermal environment in the heat exchanger and nearly adiabatic space in the tube leads to effective temperature jumps at the tube boundaries.The main goal of this paper is to numerically investigate the periodic field in thermal buffer tubes with axisymmetric geometry of thermoacoustic Stirling heat engines. The effects of variable geometry (tapered and uniform cross-section tube) and turbulence on the streaming intensity in viscous compressible oscillating flow is studied. First, one-dimensional wave equation based on Rott's assumptions in thermal buffer tube is solved by using DeltaEC software. The, hereby determined boundary and initial conditions are employed to investigate the processes by a commercial numerical solver. The simulation is carried out for straight and tapered axisymmetric tube with a pressure-based PISO solver. The results indicate that one may control the streaming effect by changing the duct geometry. Besides, it's showed that turbulence and gravity have an effective roll in reducing secondary flow.