VORTEX SHEDDING AND PERIODIC COMBUSTION PROCESSES IN A RIJKE TYPE PULSE COMBUSTOR

This paper presents the initial results of an investigation of the mec hanism that controls the operation of a Rijke type pulse combustor wit h tangential reactant injection. The study is focused on the role play ed by reacting vortices, generated in the initial section of the shear layers of the injected reactant how, upon the driving of the pulsatio ns. Detailed spatial distributions of the reaction rates were obtained by an intensified imaging system. They reveal that reacting, vortex-L ike, structures are formed near the region where the reactants enter t he injection duct when the combustor pressure is near its minimum. Sub sequently, these reacting structures grow in size and merge with each other. The merging process is accompanied by a dramatic increase in th e reaction intensity that occurs when the combustor pressure reaches i ts maximum. This satisfies Rayleigh's criterion for driving pulsations by a heat addition process. In contrast, images obtained when the com bustor is operated in a steady mode contain no periodic coherent struc tures.