Characterizing the Effect of Radial Vane Height on Flame Migration in an Ultra Compact Combustor

Abstract

The Ultra Compact Combustor (UCC) has shown viable merit for significantly improving gas turbine combustor performance. UCC models for small engines can provide centrifugal loading up to 4,000 gs. However, as the scale of the combustor increases, the g-load will necessarily decrease and the radial vane height will increase. Thus, the importance of understanding flame migration over increasing radial vane heights is pivotal to the applicability of this design to larger engine diameters. The Air Force Institute of Technology’s Combustion Optimization and Analysis Laser laboratory studied this effect with a sectional UCC model using three different vane heights. By varying the mass flow rates of the circumferential UCC section, the g-loading was varied from 500–2,000 gs. Two-line Planar Laser Induced Fluorescence at 10Hz was used for 2D temperature profiles. High-speed video at 2kHz was also used for qualitative flame migration characterization. Several cases were studied varying the radial vane height, the circumferential g-load, and the UCC/core mass flow ratio but specifically focusing on the interaction between matching the core mass flow and the core freestream velocity among the different vane heights. Finally, the decreased core flow velocity for the same mass flow weakened the shear layer between the main and cavity flows and this allowed deeper flame migration into the core flow from the UCC. Control of the overall flame migration is the key to produce desirable combustor exit temperature profiles. Increased spans lead to higher velocity gradients and increased flame injection angles at the same mass flow rates. However, at the same core flow velocities and UCC to core flow velocity ratios the flame injection angle was relatively independent of the radial vane height and almost entirely dependent on the core flow velocity alone.