Experimental Study on the Effect of Velocity Fluctuation on Flow and Thermoacoustic Dynamic Characteristics of a Self-excited Instability Flame
In order to analyze the influence of inlet velocity perturbation frequency on self-excited instability combustion and to understand the methods of suppressing self-excited instability com-bustion by velocity perturbation,the impact of velocity perturbation frequency on the flow-thermal-acoustic dynamic characteristics under self-excited instability combustion conditions was experimen-tally investigated.The experiments were conducted at room temperature and atmospheric pressure,with an inlet bulk velocity of 10.1 m/s,a velocity perturbation amplitude of 10％,and a velocity perturbation frequency range of 55 Hz to 235 Hz.The global flame heat release rate and pressure dynamic characteristics were measured using a photomultiplier tube and dynamic pressure sensor,with a sampling rate of 20 kHz.High-frequency PIV was used to measure the flow field dynamic characteristics,with a sampling rate of 1 kHz.Under the condition of self-excited instability com-bustion,the unstable frequencies of the flow-thermal-acoustic were the same,driving the self-excited instability combustion through multi-physical field coupling.When velocity perturbation was cou-pled with self-excited instability combustion,the velocity perturbation frequency was approximately equal to the self-excited instability frequency or its multiple,which inhibited self-excited instability combustion.However,at other velocity perturbation frequencies,self-excited instability combustion still dominated.When the forced combustion Strouhal number Stf was much smaller than the self-excited instability combustion Strouhal number St,the large-scale vortex of the main stage jet shear layer still existed and the vortex shedding frequency remained equal to the self-excited instability frequency.When Stf was approximately equal to or greater than St,the large-scale vortex grad-ually decreased with increasing Stf,and the vortex shedding frequency was equal to the velocity perturbation frequency
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