Effects of different active control strategies on combustion instability decay time, actuator voltage, and damping ratio

Abstract

This article numerically investigates the effects of different control strategies on combustion instability (also known as thermoacoustic instability) based on a lean-premixed combustor. Combustion instability occurs in the combustor with a sound pressure level of 51 Pa and an oscillation frequency of 271 Hz. Experimental results and the geometric data of the unstable combustor were modeled for thermoacoustic instability active control. Four types of controllers were used, and differences among control strategies were explored by comparing the “damping ratio,” “maximum actuator voltage,” and “decay time” of the active control. Results indicate that the nonlinear controller can promptly and effectively suppress thermoacoustic instability, but its actuator overshoots after triggering. The regular linear controller could not effectively suppress thermoacoustic instability. Its damping ratio was 60% compared to the damping ratio of the other controllers, and its decay time was longer than those of the other three controllers. The variation tendency of the actuator output voltage was nearly similar to that of sound pressure. The phase-shift controller had a minimum “maximum actuator voltage” of 25.6 mV under limit cycle states. The damping characteristics of the four controllers may have depended on decay time. The nonlinear controller had a minimal decay time of 0.052 s under limit cycle states. This study compared the effects of different active controllers on combustion instability and may contribute to preventing thermoacoustic instabilities in gas turbines.