Experimental studies on self-sustained combustion oscillation characteristics and flame/flow dynamics in a turbulent premixed annular combustor with different swirler configurations

This study experimentally investigates how different swirler configurations influence self-excited combustion instabilities in a turbulent premixed annular combustor across various operating conditions. The effects of swirl intensity and swirler position on flame and flow dynamics are explored in detail. Results show that swirler configurations significantly alter flame shape, height, recirculation zone structure, and vorticity distribution. Four distinct combustion regimes are identified: stable, intermittent oscillations, limit-cycle oscillations, and beating oscillations. As the equivalence ratio is varied, the combustion state is evolved along specific paths. However, the evolution patterns exhibit noticeable differences under different swirler configurations. High-speed synchronized PIV and OH* chemiluminescence imaging reveal two types of flame motion. One type (i.e., Mode I) features strong axial “pumping” driven by convective flow, involving heat release pulsations and downstream flame retraction. The other type (i.e., Mode II) shows weaker axial oscillations, primarily induced by vortex structures moving periodically along the inner shear layers. A statistical investigation on Mode I confirms a linear relationship between the pumping duration and the convective time scale, highlighting the dominant role of axial convection. Swirler configuration is found to modulate the convective time scale, thereby influencing velocity fluctuations and ultimately determining oscillation frequency. Finally, we show that the fundamental combustion properties of the fuel have minimal impact on the dynamic behavior of Mode I in this annular combustor.