Suppression of Combustion Instabilities in a Premixed Swirl Combustor with Acoustic Liner

Abstract

Acoustic liner is one of effective passive control methods of combustion instabilities. This paper presents an experimental investigation about the suppression of the combustion instabilities using acoustic liners. A premixed swirling combustor was built and a specially designed acoustic liner was set at the downstream of the flame zone. Then, experiments of rigid wall, acoustic liner without and with tunable bias flow were carried out respectively. Furthermore, considering the viscous dissipation of airflow is temperature related, the temperature of the bias flow was adjusted in order to evaluate its effects on thermoacoustic instabilities. The bias flow was heated by electric taps before entering the acoustic liner in this rig. Results shows that the unstable Helmholtz mode could be triggered, and the oscillation amplitude grows with the increase of the bias flow Mach number, while the instability of 1/4 wavelength mode may be completely suppressed. Within the scope of the experiments, the unstable Helmholtz mode triggered by the bias flow can be attenuated by raising the bias flow temperature, while no substantial changes are observed about the quarter wave mode. These results are rarely reported in previous studies. Studying the effects of acoustic liner on combustion instabilities can provide useful knowledge regarding its application in real combustion systems. NOMENCLATURE V Volume flow rate (slm) Ф Equivalence ratio (-) Wc Combustion power (kW) T Temperature (K) τ Time delay Ma Mach number y Axis coordinate of the burner (mm) P′ Amplitude of acoustic pressure (Pa) f Freqency (Hz) acpr Acoustic pressure from COMSOL (Pa) SNR Signal to noise ratio slm Standard litre per minute (L/min)