Date of Award

3-21-2019

Document Type

Thesis

Degree Name

Master of Science in Aeronautical Engineering

Department

Department of Aeronautics and Astronautics

First Advisor

Marc D. Polanka, PhD

Abstract

The Ultra Compact Combustor (UCC) promises to greatly reduce the size of a gas turbine engine’s combustor by altering the manner in which fuel is burnt. Differing from the common axial flow combustor, the UCC utilizes a rotating flow, coaxial to the engine’s primary axis, in an outboard circumferential cavity as the primary combustion zone. The present study investigates two key UCC facets required to further this combustor design. The first area of investigation is cooling of the Hybrid Guide Vane (HGV). This UCC specific hardware acts as a combustor center body that alters the exit flow angle and acts as a secondary combustion zone. As improved UCC designs yield higher operating temperatures, cooling of this component must be considered. Previous numeric efforts determined the viability of a passive cooling scheme where cooler compressor air was drawn into an opening at the stagnation region of the HGV and used for both internal and film-cooling of the vane. The present study experimentally investigated the performance of five cooled HGV configurations, each having a unique combination of film-cooling, internal passage area, and internal passage geometry, over a range of flow conditions. Results confirmed the efficacy of HGV cooling via passive air ingestion. The internal vane geometry affected both internal coolant mass flow and pressure rise offering a means to adjust both parameters based on cooling requirements. Vane internal to external pressure differential had a strong impact on blowing ratio where low differences provided sub-optimal cooling benefits and large differences caused the coolant jet to penetrate into the freestream, altering its flow structure. Next, the UCC hardware was modified to accommodate enhanced combustor diagnostics. Previous studies relied on point measurements or optical analysis of a small portion of the cavity greatly limiting the obtainable data. By replacing the rear enclosure of the combustor with a clear quartz back plate, analysis of the flow dynamics in the entire cavity was made possible. Design features that ensured a sealed combustor while still accommodating thermal expansion of the quartz allowed extensive data to be collected while avoiding damage to the modified hardware. These modifications were then leveraged to assess the underlying complex aerodynamic and combustion phenomenon driving previously observed average combustor exit temperatures. Emissions of OH and CH radicals were recorded using intensified relay optics and a high speed camera providing information on flame location. Tracking the flame’s movement enabled its velocity within the cavity to be determined. Observed average cavity tangential velocity increased with cavity airflow rate and had the highest local value within the cavity, near the step air injection. Velocity was lowest at the vane tips of the HGV, which locally disrupted flow migration. Increased tangential velocities adversely affected the ability of the flame stabilizing mechanism to anchor a flame, resulting in less overall flame activity at higher cavity velocities. This was primarily driven by the method of air injection which, at all but the lowest tangential velocities, prevented flow recirculation in half of the stabilizing zones. Further increase in cavity tangential velocity altogether pushed the flame off of the outside diameter of the combustor, which temporarily stabilized around the HGV prior to extinguishing. Lastly, analysis of combustion event movement indicated larger tangential velocities decreased residence time coinciding with a previously observed drop in average combustor exit temperature.

AFIT Designator

AFIT-ENY-MS-19-M-239

DTIC Accession Number

AD1074068

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