| Summary: | <p>Regulatory pressures aimed at reducing NOx and particulate emissions from civil aviation have seen engine manufacturers gravitate towards lean-burn combustor architectures. Compared to their conventional <em>rich-burn</em> counterparts, lean-burn combustors generate significant swirl and alter the temperature distribution at the interface with the high-pressure turbine. We examine the impact of lean-burn on the aerothermal performance of high-pressure nozzle guide vanes (NGV), leveraging engine-scale experiments and simulations.</p>
<p>Experiments were conducted in the Engine Component AeroThermal facility—an annular NGV test facility designed to operate at engine-matched conditions of Mach number, Reynolds number, and coolant flow. Two test cases were considered: a reference case with uniform inflow, and a lean-burn case, which used a combustor simulator to generate representative inlet profiles of swirl and temperature distortion. Mean-flow and turbulence conditions <em>upstream</em> of the NGV were characterized in detail using a purpose-built traverse system. These served as reference conditions for measurements of flow angle, kinetic energy loss, and total temperature taken <em>downstream</em> of the NGV, and were used as inlet boundary conditions in complementary simulations.</p>
<p>In a first instance, turbulence model sensitivities were explored, using the experimental dataset with uniform inflow as a benchmark. Simulations based on the <em>k–ω</em> shear stress transport model captured radial distributions of whirl angle, loss, and non-dimensional temperature reasonably well, but failed to accurately predict mixing rates of the aerodynamic and thermal wakes. Undermixing is a common problem in simulations of flows where significant unsteady vortex shedding <em>occurs</em> in reality, but is not <em>modeled</em> due to steady-state assumptions. For the current geometry and inlet conditions, the baseline <em>k–ω</em> algebraic Reynolds stress model had enhanced free shear mixing, resulting in a slightly better overall collapse with experimental data.</p>
<p>In a second instance, the effect of lean-burn was studied. Compared to the uniform inflow reference case, lean-burn caused significant residual swirl in the downstream flow, and amplified integral loss slightly. Changes in the downstream thermal field were primarily driven by the upstream temperature profile, with a secondary influence from swirl-induced redistribution of vane coolant. Coolant redistribution was especially pronounced on the vane pressure side, where uneven film coverage led to significant deterioration of cooling performance.</p>
<p>This thesis represents a comprehensive analysis of the impact of lean-burn on NGV performance, gives insight into the robustness of commonly-used simulation tools, and highlights areas for redesign to optimize for lean-burn profiles.</p>
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