CFD Modeling of Combustion Instability in Premixed Axisymmetric Combustors

Time-accurate CFD analysis is used to model combustion instability in a premixed axisymmetric combustor typical of industrial gas turbine engines. The experiment of Richards and Janus (1997) is modeled; the hardware consists of a fuel injector similar to industrial premix fuel nozzles, a water-cooled can combustor, an uncooled refractory plug that reduces flow area, and a long exhaust duct. The CFD calculation domain extends from the air swirler within the fuel nozzle to the exhaust duct exit. Two cases are modeled using 2D time-accurate axisymmetric CFD analysis: a low nozzle air velocity (u = 30 m/s) case that exhibits combustion instability and a high nozzle air velocity (u = 60 m/s) case that does not. The CFD analysis agrees well with the experimental measurements, including peak-to-peak pressure variation and instability frequency for the unstable case. For the unstable case, the airflow through the swirler actually flows upstream part of the time, and hot combustion products are forced into the premix annulus. The potential of using a time-accurate CFD approach for modeling combustion instability in complex 3D combustors is discussed.Copyright © 1997 by ASME