Characterization of Axial Turbines for Pressure Gain Combustion
Pressure gain combustion is beneficial for engine cycle efficiency, compactness, and less emissions. In this disseration, two classes of fluid expansions systems were developed to harness power from the high-speed flow delivered by the pressure gain combustor: a compact expansion system and an efficiency expansion system. In addition, a new class of pressure probes for expansion systems is developed.
A numerical methodology is carried out to design and characterize these expansion devices and measurement systems via steady and unsteady Reynolds Averaged Navier stokes simulations. Firstly, the compact expansion system is achieved by developing a supersonic axial turbine. Performance of the supersonic axial turbine exposed to fluctuations from a nozzle downstream of a rotating detonation combustor is assessed with an increased level of complexity, including time-resolved stator, time-resolved rotor, and time-resolved turbine stage characterization. Power extraction, damping of fluctuations, and loss budgeting are evaluated. Unsteady heat transfer assessment is performed to investigate the convective heat flux distribution and decomposition. A performance map is constructed to explore the operating limit. Afterwards, the efficient expansion system is achieved by retrofitting an existing subsonic axial turbine. Without redesigning turbine airfoils, the stator endwall contour was modified to integrate the subsonic axial turbine to a diffuser and a rotating detonation combustor. Performance of the retrofitted subsonic axial turbine exposed to fluctuations form a diffuser is evaluated at several frequencies, amplitudes and inlet Mach numbers, with an increased level of model fidelity, including unsteady stator alone, unsteady turbine stage with a reduced model, full unsteady turbine stage assessment. Turbine efficiency, damping of oscillations, and loss budgeting are assessed. A multi-step optimization strategy is utilized to enhance turbine efficiency by improving the endwall contouring. A performance map is created to examine the operating range. Finally, a new type of pressure probes was developed and angular calibration was performed. A whisker-inspired design enabled the reduction of the vortex shedding effect.