58947 - Low-Order Modeling of Can-Annular Combustors 

Heavy-duty land-based gas turbines are usually designed with can-annular combustors, which consist of a set of independent cans. The cans are acoustically connected with each other on the upstream side via the compressor plenum, and downstream with the annular gap located at the transition with the first turbine stage. The modeling of this cross-talk area is crucial to predict the thermo-acoustic modes of the system. Because of the discrete rotational symmetry of such combustors, Bloch wave theory can be used to reduce the system to a simple longitudinal combustor with a complex-valued equivalent outlet reflection coefficient that models the annular gap. In the present study, we review the recently proposed models based on the Rayleigh conductivity and on a thin-annulus description respectively and compare them to 2D Helmholtz simulations. We demonstrate that the modeling of the gap with a thin annulus is not suited for can-annular combustors whereas the Rayleigh conductivity model gives good qualitative results. We then propose a new model for the equivalent reflection coefficient based on a characteristic length. We show that such a model gives not only qualitative but also quantitative agreement compared to 2D results. We then perform a Design of Experiments which allows us to explore various configurations, find the validity limits of our model and build correlations.