CFD моделювання розвитку термоконвекційних течій на процеси запуску низькотемпературних термоакустичних двигунів

Thermoacoustic engines (TAEs) represent a promising solution for the efficient conversion of low-grade heat into acoustic energy and mechanical work. A major challenge for their practical implementation is the need to ensure reliable startup, i.e., stable self-excitation of thermoacoustic oscillations. This study aims to identify methods that ensure the guaranteed startup of TAEs. Theoretical convective effects play a key role in the onset of self-sustained thermoacoustic oscillations. The object of this study is the development of thermoconvective flow, while the subject is the characteristics of its vortex structures, particularly their scales and frequencies. To investigate the thermal processes involved in TAE startup, CFD modeling was performed. The main task was to develop, verify, and validate a three-dimensional unsteady numerical model of a TAE operating in a standing wave configuration. The simulation employed original experimental data, specifically, temperature trends of the engine’s key structural components. Results. For the first time, it was experimentally confirmed and validated by CFD calculations that a longitudinal temperature gradient in the TAE core is a necessary but insufficient condition for the onset of thermoacoustic oscillations. Thermoconvective flows are formed in the TAE resonator as vortex structures with various frequencies and scales. It was also established that vortex structures arise with frequencies matching the engine’s natural resonance frequency under certain conditions. Conclusions. The experimental results indicate that the heaters’ dynamic characteristics, particularly their thermal inertia and heating rate, significantly influence startup efficiency. In low-temperature TAEs for energy-saving applications, the use of auxiliary heaters is advisable because they promote the formation of intense thermoconvective flows. The outcomes of this study support the practical implementation of thermoacoustic systems for using low-temperature heat sources, whether waste or renewable.