Thermoacoustic instability, caused by the interaction of unsteady heat release and acoustic waves, is a significant challenge in combustion systems such as gas turbines and aero engines. To identify instability thresholds, this study investigates thermo-acoustic instability in a horizontal
Rijke tube through experimental measurements and two-dimensional computational fluid dynamics (CFD) simulations. The study focuses on the effects of heat source positioning and boundary conditions, which are critical for optimising combustion system design. A heat source was placed at one-quarter of the tube’s 800 mm length, and pressure oscillations were measured 150 mm from the heat source. Acoustic frequencies and sound pressure levels (SPL) were used to identify the instabilities. This study is unique in that it combines experimental and CFD approaches
to systematically analyse the effects of heat source positioning and boundary conditions. The results show a strong agreement between experimental and simulated acoustic frequencies (216 Hz vs. 215 Hz), and the simulated values were set at a higher level to simplify the boundary condition. These results demonstrate the importance of accurate heat source positioning, appropriate specification of boundary conditions, and obtaining sufficient boundary-condition data. This study highlights the key mechanism related to the positioning of the heat source and the
prescribed boundary condition in thermoacoustic instability. In addition, it proposes strategies to improve CFD models, reduce instabilities, and enhance the performance, efficiency, and safety of combustion systems.