Effect of Trapped Vortex Combustion with Radial Vane Cavity Arrangements on Predicted Inter-Turbine Burner Performance

The complex combustion processes, including chemical reactions, turbulence, unsteady, multiphase flow, evaporation and heat and mass transfer pose great challenges in modern propulsion system design and development. Ultra-short compact, high performance combustion systems are desirable for advanced propulsion systems from the standpoint of lower fuel consumption and increased material durability. AFRL has proposed placing an Ultra-Compact Combustor (UCC) between a high pressure turbine stage and low pressure turbine stage to create an innovative Inter-Turbine Burner (ITB) concept. This paper focuses on ITB combustor technologies that can enable the development of compact, highperformance combustion systems. Compact combustors weigh less and take up less volume in space-limited turbine engine for aero applications. The earlier designs conceived and developed at AFRL/RZTC is based on the idea that the flame speed under turbulent conditions is directly proportional to the square root of gravity and high-g flames offer increased flame speeds, which would aid in the design of shorter combustion systems. This idea led to an ITB with a circumferential cavity in which fuel and air injected at selected points led to rich combustion in the circumferential cavity. This was further followed by lean combustion and flame stabilization with the aid of a radial vane with notch. Even though this concept exhibited good merits through several rig tests and numerical studies carried out over the years at AFRL/RZTC, it does not allow scaling of the geometry and configuration for higher mass flow rates, larger size and increased thrust requirements. This paper presents an alternative concept for the UCC that uses a Trapped Vortex Cavity (TVC) to replace the high swirling circumferential cavity combustion to enhance mixing rates via a double vortex system in the TVC, followed by further mixing of the free stream air through the vane with a notch. Flow field predictions utilizing FLUENT are presented for concept evaluation in a systematic way to understand the flow development and physics, leading to the incremental combustion enhancement, total pressure loss, the entrainment and the calculated exit temperature profile. The analysis supplements the understanding of the design space required for future engine designs that may use this novel, compact combustion systems.