Compressor/diffuser/combustor aerodynamic interactions in lean module combustors

The paper reports an experimental investigation into the possibility of increased interactions between combustor external aerodynamics and upstream components e.g. pre-diffuser, compressor OGV and even the compressor rotor, caused by the trend in lean module fuel injectors to larger mass flows entering the combustor cowl. To explore these component interaction effects, measurements were made on a fully annular rig comprising a single stage compressor, an advanced integrated OGV/pre-diffuser, followed by a dump diffuser and a generic combustor flametube with metered cowl and inner/outer annulus flows. The flow split entering the cowl was increased from 30% to 70%. The results demonstrate that, with fixed geometry, as the injector flow increases, the performance of the pre-diffuser and feed annuli suffer. Pre-diffuser losses increase and at high injector flow rates the diffuser moves close to separation. The substantial circumferential variation in cowl flow can feed upstream and cause rotor forcing. Notable differences in performance were observed inline and between injectors at OGV exit, suggesting that geometry changes such as an increased dump gap or non axisymmetric pre-diffuser designs may be beneficial.