                Prior research into Ultra Compact Combustors (UCC) showed an axial length savings compared to traditional gas-turbine combustors. This savings is achieved by swirling the reactants circumferentially in a recessed cavity around the outside diameter of the engine. A similar circumferential combustor is envisioned for a new engine configuration that positions the combustor outboard of a radial compressor and an inflow turbine. This configuration will not only offer an axial length savings from the combustor, but for the entire engine as well.  Prior UCC configurations utilized a diffuser to split air from a common upstream flow source into a core flow and a cavity flow. The core flow air continued axially and bypassed the combustor. The cavity air was forced into the circumferential combustor cavity through angled holes to drive the reactants in a circumferential direction to burn under enhanced centrifugal load. The combustion products were then exhausted radially inward and mixed with the core flow air prior to entering an axial turbine rotor.  The new engine configuration will not utilize a core flow path and thus requires all engine air from the compressor to pass through, or around, the combustor cavity. This report characterizes the cavity flow behavior as the core flow quantity was reduced from 80% of the total engine mass flow rate down to zero, representing the new engine configuration, while maintaining constant cavity mass flow rates. Velocity profiles were obtained with shadow particle image velocimetry (PIV) using phenolic micro-balloons in cold flow and with particle streak emission velocimetry (PSEV) with silicon carbide particles in reacting flow experiments. The cold flow results showed that the core flow produced a suction by flowing below the circumferential cavity and removed fluid resulting in a lower mass flow rate. This behavior resulted in lower circumferential velocities at higher core flow percentages and the fastest cavity velocity with zero core flow. Reacting flows produced a less straightforward result with the fastest cavity velocities achieved at reduced, but non-zero core flows, and the slowest velocities at the highest and zero core flow amounts. Overall, it was found that that there is no negative impact on cavity performance from the removal of the core flow that would prohibit development of the new engine configuration. For use of this flow geometry without core flow, the additional engine mass flow rate would be required to flow around and bypass the combustor to provide cooling and to be reintroduced as dilution air just upstream of the turbine.       

 


Circumferential Combustor Cavity Flow Fields With Decreasing Core Flow

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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