COMBUSTION OSCILLATIONS IN A TWIN-STREAM AFTERBURNER

In a modern turbo-fan engine, the afterburner flame-holders are positi oned in the mixing flow between the core and bypass streams. These two streams have different velocities and temperatures. They also have di fferent duct lengths and, therefore, different acoustic properties. Th e influence of such a twin-stream supply on acoustically coupled combu stion oscillations is investigated in this paper. Measurements on an e xperimental rig show how differences in the acoustic impedances, the m ean velocities and the mean temperatures in the two supply streams lea d to appreciably different unsteady heat release rates in the two stre ams. These affect the frequency of the combustion oscillation. A theor y explains these results and correctly describes the variation in freq uency as the properties of the two supply streams are varied. (C) 1995 Academic Press Limited