Effect of lean-burn combustor outlet flows on nozzle guide vane aerothermal performance: an experimental and computational study

Thesis

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 rich-burn 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.

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 upstream 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 downstream of the NGV, and were used as inlet boundary conditions in complementary simulations.

In a first instance, turbulence model sensitivities were explored, using the experimental dataset with uniform inflow as a benchmark. Simulations based on the k–ω 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 occurs in reality, but is not modeled due to steady-state assumptions. For the current geometry and inlet conditions, the baseline k–ω algebraic Reynolds stress model had enhanced free shear mixing, resulting in a slightly better overall collapse with experimental data.

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.

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.

Authors: Amend, JE

• DOI: 10.5287/ora-exx0z1xng
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: aerodynamics; experimental; simulation; nozzle guide vane; transonic; heat transfer; lean burn; combustor turbine interaction; turbine
• Subjects: Turbomachinery