Control of Azimuthal Combustion Instability Through the Injector Mounting Surface of Annular Combustors

Abstract

A three-dimensional combustion instability model is presented to study the effects of the wall impedance distributions of annular combustors on thermoacoustic unstable modes, consequently seeking an effective passive methodology to suppress azimuthal combustion instability. The eigenfunction is obtained by use of Green’s function in an enclosed space, whereas the scattered disturbances at flames, the perforated screen where the injectors are installed, and the side perforated liner are characterized by the monopoles, respectively. Results show that compared to the side perforated liner with the restriction of radial size, the impedances over the injector mounting surface provide more acoustic energy dissipation to suppress the azimuthal combustion instabilities. Two patterns of impedance distribution, uniform and radial nonuniform, over the injector mounting surface are then investigated through the parametric variations and associated acoustic energy analysis. A stable combustion system can be realized in combination with homogeny or difference between the spatial impedance distributions and associated optimum perforated parameters, such as perforation ratio, Mach number of the mean bias flow, and aperture radius. It allows mitigating possible design limitations with the appropriate parameter combinations. The present investigation thereby offers an alternative model and methodology for suppression of azimuthal combustion instabilities in gas turbines.