Helical Flow Disturbances in a Multinozzle Combustor

This paper describes an experimental investigation of a transversely forced, swirl stabilized combustor. Its objective is to compare the unsteady flow structures in single and triple nozzle combustors and determine how well a single nozzle configuration emulates the characteristics of a multinozzle one. The experiment consists of a series of velocity field measurements captured on planes normal to the jet axis. As expected, there are differences between the single and triple nozzle flow fields, but the differences are not large in the regions upstream of the jet merging zone. Direct comparisons of the time-averaged flow fields reveal a higher degree of nonaxisymmetry for the flow fields of nozzles in a multinozzle configuration. Azimuthal decompositions of the velocity fields show that the transverse acoustic forcing has an important influence on the dynamics, but that the single and multinozzle configurations have similar forced response dynamics near the dump plane. Specifically, the axial dependence of the amplitude in the highest energy axisymmetric and helical flow structures is quite similar in the two configurations. Thus, upstream of the jet merging zone, the hydrodynamic influence of one swirling jet on the other is minimal. As such, that jet–jet interactions in this configuration do not have a significant influence on the unsteady flow structures.