Noncircular Inlet Duct Cross-Section to Reduce Combustion Instabilities

Abstract

The unique shear-flow characteristics of a triangular jet were used to suppress longitudinal pressure oscillations in a coaxial dump combustor. The asymmetric flow configuration enhanced fine-scale mixing in the corner flow, while maintaining large-scale mixing at the flat sides, as demonstrated in air and water flows with and without forcing. In a forced annular diffusion flame it was shown that the flat-side shear layers were dominated by reacting vortices which lead to periodic heat release and possible driving of pressure oscillations, while the combustion at the corners was more intense and free of periodicity because of highly three-dimensional flow with enhanced molecular mixing between the fuel and oxidizer. For a coaxial dump, the pressure oscillations were significantly reduced with a triangular inlet duct and corner injection, compared to a triangular inlet duct with flat-side injection and to a circular inlet duct.