Analysis of Highly Swirled, Turbulent Flows in Dump Combustor With Exit Contraction

Abstract

Highly swirled flows are commonly used in gas turbine combustors to stabilize the flame and enhance fuel-air mixing. Experiments by D. G. Lilley, 1985 have shown that swirling flow patterns (i.e. recirculation zones) are dramatically impacted by a downstream contraction. For unconstricted swirling flow, a large, central recirculation zone is formed, while for constricted swirling flows, the recirculation zone can be annular in shape and high (positive) axial velocity is seen on the centerline of the combustor. Over the past 20 years, steady-state Reynolds Averaged Navier Stokes (RANS) solutions with various turbulence models have not been able to mimic the flowfield patterns for swirling flow with a downstream contraction. In this study, Large Eddy Simulation (LES) calculations were performed that correctly predicted the recirculation flow patterns for swirling flow with a downstream contraction. In addition, LES predicted radial profiles of swirl velocity agreed well with measurements, including the solid body vortex core on the centerline of the combustor. RANS produced inferior predictions. Two cases with 45° swirlers and a dump combustor with and without a downstream contraction were modeled. The LES predictions were compared with RANS predictions and Lilley’s measurements. The computational domain included flow through the swirl vanes, the combustor, and the contraction area. The unstructured, parallel CFD-ACE+ code was used, with the Localized Dynamic kinetic Energy Model (LDKM) for subgrid turbulence.