Mechanisms for Enhanced Flow Migration from an Annular, High-g Ultra Compact Combustor

Abstract

The Ultra Compact Combustor (UCC) is novel solution to address the challenge of improving gas turbine engine performance. The “high-g” UCC design operates by diverting a portion of axial compressor flow into a circumferential combustion cavity positioned about the engine outer diameter. The cavity provides the necessary residence length and time for combustion within substantially reduced axial lengths; furthermore, high g-loads are induced by the cavity bulk circumferential swirl; these conditions have been shown to substantially reduce flame lengths and improve lean blow-out performance. Experimental work at the Air Force Institute of Technology (AFIT) has facilitated the evolution of an atmospheric UCC test rig with a wide range of capabilities and with established operating maps. Recent work has highlighted an issue with effectively migrating the hot gases out of the combustion cavity radially along a hybrid guide vane. A comprehensive numerical evaluation was accomplished to examine the effects of two potential design iterations. First, the hybrid guide vane geometry was modified to incorporate a radial vane cavity (RVC). The modification was successful in redistributing peak temperatures at the combustor exit at the expense of reduced profile uniformity. The net effect of the RVC, based on combustion efficiency, was negative in lean-cavity conditions, but improved in rich-cavity conditions. The second design change incorporated compound-angle cavity air drivers. Results indicated the compound drivers improved mixing and efficiency within the cavity, consequently encouraging more complete combustion through the remainder of the system. The benefits of the compound air drivers were conclusive, however the design of the RVC will require further study in order to better shape the exit temperature profiles.