Abstract
A gas-kinetic scheme (GKS) based on an unstructured grid is applied to simulate the evolution of the fluid motions in exponential variable cross-section resonators. The effects of the acoustic field intensity on the oscillatory pressure, velocity, temperature, and flow streaming structure were investigated numerically, and the model was validated. The results demonstrate that the geometry and driving strength are the main factors affecting the final performance of the system. For the quasi-linear and moderate non-linear cases in optimum exponential tube, the periodic generation, evolution, and shedding of vortices in flow fields are associated with the storage and release of energy, which is the transmission mode of the third type of direct current (DC) flow, and its driving mechanism is attributed to the asymmetrical pressure and temperature. Meanwhile, some new physical characteristics were also discovered for the highly non-linear case, e.g., the disorder and unsteadiness of the flow direction accomplished with turbulent flow streaming structures. The secondary flow is manifested as multiscale, irregular and unsteady vortices throughout the tube. The smallest increment of pressure and velocity amplitude occurs concurrently with the biggest increment of temperature amplitude. These evidences suggest that there is an optimal driving strength, even for a good configuration tube, with which the maximum efficiency can be obtained.
Highlights
Owing to its high reliability and environmental friendliness, thermoacoustic engines without moving parts have attracted increasing attention as a major technology to develop more efficient energy conversing or generating systems [1,2]
The working gas in thermoacoustic engines is characteristic of the alternating current (AC) gas flow, which alternately moves backward and forward with pulsating pressure at certain frequencies
Some numerical experiments are carried out for an m = 2.2 exponential-shaped resonator under five different driving strengths, which lead the acoustic fields to change from quasi-linear to highly non-linear
Summary
Owing to its high reliability and environmental friendliness, thermoacoustic engines without moving parts have attracted increasing attention as a major technology to develop more efficient energy conversing or generating systems [1,2]. Researchers have been focusing on developing measures and approaches to suppress these non-linearities [3,4]. It is well-known that one can obtain high-amplitude and shock-free acoustic oscillations by varying the shape of resonators. This method was first presented by Lawrenson et al [6] and is called resonant macrosonic synthesis (RMS). Luo et al [7]
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