Generation and Alleviation of Combustion Instabilities in Swirling Flow

Abstract

Most gas turbine and other combustion systems use swirl as a methodof flame stabilization. Swirling flows can in themselves generateseveral different types of flow and flame instability, as well asfacilitating coupling with natural acoustic modes of a system. Thispaper reviews recent work in the area and describes how fluctuationin the structure of the recirculation zone and tangential coherentstructures (precessing vortex core [PVC]) can generate structuresin other planes, capable of giving periodic heat release and excitationof combustion instability via the Rayleigh criterion. This is relatedto combustion-driven oscillations in gas turbine combustors. It isshown how damping of these tangential coherent structures can occurvia certain modes of combustion whilst appropriate acoustic couplingcan reexcite these phenomena. Methodologies for alleviation of theseeffects are described.