In the era of carbon neutrality, thermoacoustic instability poses significant challenges to the development of combustion-based energy systems, particularly gas turbines. The high-amplitude self-excited flow oscillations caused by thermoacoustic instability can lead to excessive heat transfer, elevated NOx emissions, and accelerated fatigue cycling. This thesis investigates the efficacy of genetic programming (GP) in mitigating three different types of thermoacoustic oscillations: periodic, quasiperiodic and chaotic. This is done experimentally on both a flame-driven Rijke tube and an electrically-heated Sondhauss tube. Both closed-loop and open-loop forms of GP control are tested. The results show that for all three types of oscillations, GP closed-loop control can outperform other con...[ Read more ]

In the era of carbon neutrality, thermoacoustic instability poses significant challenges to the development of combustion-based energy systems, particularly gas turbines. The high-amplitude self-excited flow oscillations caused by thermoacoustic instability can lead to excessive heat transfer, elevated NOx emissions, and accelerated fatigue cycling. This thesis investigates the efficacy of genetic programming (GP) in mitigating three different types of thermoacoustic oscillations: periodic, quasiperiodic and chaotic. This is done experimentally on both a flame-driven Rijke tube and an electrically-heated Sondhauss tube. Both closed-loop and open-loop forms of GP control are tested. The results show that for all three types of oscillations, GP closed-loop control can outperform other control strategies, including GP open-loop control and conventional open-loop control. For periodic oscillations, synchronization analysis of the coupling between the acoustic pressure and the heat release rate in the Rijke tube reveals the occurrence of weak intermittent phase synchronization during control actuation. Moreover, the suppression of such oscillations in the Sondhauss tube is found to occur via synchronous quenching, in contrast to the conventional mechanism of asynchronous quenching found in the Rijke tube. Crucially, for both periodic and aperiodic thermoacoustic oscillations, it is found that the optimal control law identified by GP is that which imposes actuation at the preferred mode of the open flame, corresponding to the global maximum of the flame describing function. Regardless of the oscillation type, GP closed-loop control is always found to yield the lowest cost function value, with substantial amplitude reduction (> 90%) at minimal actuation power. As the world moves towards carbon neutrality, there is a growing need for sustainable energy systems that can operate efficiently, reliably and economically. The use of GP offers a potential solution to this challenge by providing an effective strategy for suppressing thermoacoustic oscillations in various combustion devices, including those that burn carbon-free fuels such as hydrogen.