Numerical investigation on the porosity effect of a bias-flow perforated liner on attenuating self-excited thermoacoustic oscillations

Abstract

Self-excited thermoacoustic oscillations are unwanted in propulsion and stationary gas turbines due to the undesirable structural and heating damage to the engine systems. To prevent overheating and damping noise, perforated liners are widely applied in engines. It is a cylindrical metal sheet perforated with a number of millimetre-size circle orifices. In this work, numerical studies are conducted on an acoustically open-open thermoacoustic combustor with premixed propane and air fuelled and burnt. A perforated liner with a porosity σ is implemented downstream of the combustor in the presence of a cooling flow (also known as bias flow). The effects of (1) the cooling mass flow rate ṁb and (2) the porosity σp are examined one at a time. It is found that in the absence of the cooling flow, i.e., ṁb = 0, the perforated liner’s acoustic damping effect is quite small. Increasing is found to increase the liners damping performance in terms of attenuating the thermoacoustic oscillations, due to the enhanced vortex shedding generated over the rims of the perforated holes. In addition, there is an optimum cooling flow rate corresponding to the maximum acoustic damping effect of the liner. Furthermore, for a given mass flow rate, there is an optimum porosity.