Influence of the Acoustic Liner in Large Eddy Simulation of Longitudinal Thermoacoustic Instability in a Model Annular Combustor

Although extensive efforts have been made to dampen the thermoacoustic instability,successfully controlling the pressure oscillations in modern gas turbines or aeroengines remains challenging.The influence of the acoustic liner on the longitudinal thermoacoustic mode in a model annular combustor is investigated by Large Eddy Simulation(LES) in this work.The result of the self-excited longitudinal thermoacoustic instability without the liner agrees well with the frequency and acoustic analysis of the pressure mode based on experimental data.Three different bias flow velocities of the liner located downstream of the combustor are then simulated.The results reveal that the existence of the liner influences not only the acoustic field but also the flow field.When the bias velocity is large,it leads to intense turbulence-induced fluctuations,and the pressure oscillation is modulated intermittently.It shows that the weak coupling between flow and pressure oscillations plays a significant role in the onset of the intermittency of a thermoacoustic system.Based on the dynamic analysis of the thermoacoustic system with the acoustic liner,this intermittency is caused by the influence of the flow field on the flame-acoustic coupling.Finally,a low-order modeling method based on Van der Pol(VdP) oscillator with additive stochastic forcing is conducted to reproduce the evolving dynamics of the thermoacoustic system.Although the numerical cases demonstrated in this work are relatively simpler than those in a practical combustion system,the results are helpful for us to understand the effect of the acoustic liner and show the attractive potential to apply this device to suppress thermoacoustic instability.