Application of the Perforated Plate in Passive Control of the Nonpremixed Swirl Combustion Instability Under Acoustic Excitation

Perforated plates are widely used to attenuate noise emission and as acoustic liners in combustion chambers. In this study, the damping performance of the perforated plate located in the combustor inlet section is experimentally and numerically studied. The primary response of nonpremixed swirl flame under 30–400 Hz acoustic excitation with a 445 mm inlet length occurs at 134 Hz and 210 Hz modes. The perforated plate designed for 210 Hz sound absorption with a 328 mm cavity length and an 8.04% porosity is compared to plates with various cavity lengths and different orifice patterns. The acoustic absorption capability of perforated plates is evaluated by the Luong model and tested in an impedance tube. The acoustic measurements show that the sound absorption performance of each plate is strongly affected by the bias flow velocity and cavity length. The combustion results indicate that the installation of perforated plates at the inlet section has two effects: sound attenuation and redistribution of the pressure mode of the combustor. The acoustic mode analysis further demonstrated that, for damping the nonpremixed flame when the combustion instability is caused by the inlet pressure fluctuation, modification of the inlet acoustic mode shape is more efficient than the sound attenuation.