<p>To increase overall aircraft engine efficiency, the diameter of the high-pressure turbine is reduced, leading to low aspect ratio airfoils. Secondary flow dominates in these low aspect ratio turbines, and the small airfoil geometry inhibits flush-mounted, full-spatial dynamic pressure measurements with pressure transducers. Airfoil surface pressure measurements are vital to understanding the inherently unsteady flow phenomena in turbines. Additionally, aerodynamic performance data derived from high-resolution surface pressure measurements provide invaluable data for validating computational fluid dynamics codes used for prediction. Non-intrusive measurement techniques such as fast-responding Pressure Sensitive Paint (PSP) offer a potential solution of a full-field optical measurement of surface pressure fluctuation, with each camera pixel representing a sensor. The porous binder improves the dynamic response of PSP, making it suitable for unsteady flow environments such as turbomachinery applications. In this view, the overall objective of the current doctoral research is to develop a lifetime PSP method using laser-based excitation for surface pressure measurement on a new class of high-pressure turbines. </p> <p>The overall research goal was subdivided into three main strategies. (1) A pulse lifetime calibration procedure of a porous polymer/ceramic binder PSP was developed in a pressure-controlled chamber to assess the correlation between pressure and time-resolved luminescent lifetime, pressure sensitivity, and signal-to-noise ratio. (2) The lifetime technique was implemented for surface pressure measurements in a linear test section to measure high spatial pressure gradients and resolve unsteady flow features. A data reduction routine and an optimal binning bundle of pixels were proposed for calibration analysis to reduce the overall pressure uncertainty. Uncertainty quantification and sensitivity analysis were also completed to determine the parameters with a substantial effect on the pressure uncertainty. (3) The pulse lifetime method was demonstrated on a high-pressure turbine vane suction surface at engine representative conditions. The surface pressure data were corroborated with static pressure tappings and computational simulations. This research effort provided new insights into time-resolved luminescent lifetime PSP techniques. Steady and unsteady flow features from surface pressure measurements were identified using a precise calibration method. The lifetime pulse method was effective in a high-pressure turbine flow field, paving the way for back-to-back PSP experiments with different turbine geometries. </p>

<p dir="ltr">Tip leakage flows in unshrouded turbines lead to significant pressure losses and heat loads, both on the rotating blades and the adjacent casing surface. These penalties are influenced by the tip clearance size, highly pertinent to the new generation of small-core high-speed turbines. Tailored to decrease tip leakage effects, small-core turbines feature running clearances below 0.3mm, making small blade-to-blade clearance variations extremely relevant for the machine's performance. Therefore, tip clearance monitoring and assessment of the leakage flow structures are paramount to design strategies for this class of turbines. Due to the limitations of commercially available CFD tools to accurately resolve highly detached unsteady flows, in-situ empirical observations are required. Furthermore, the documentation of flow field relationships with the tip clearance is highly valuable for in-service engine applications, such as tip clearance estimations from more accessible measurements to provide feedback for clearance control systems.</p><p dir="ltr">The dissertation developed hereafter performs aerothermal measurements in the casing end wall of a small-core high-speed turbine at engine-representative conditions and a wide range of clearance values. A novel in-situ calibration procedure for capacitance probes is tailored to reduce the required clearance measurements and the experimental time. Its uncertainty analysis demonstrates improved prediction bands, supporting this method for tight clearance measurements. A thorough evaluation of the casing static pressure is performed with high-frequency miniature pressure transducers. Specific trends are identified with independent variations of operating pressure ratio, rotational speed, and tip clearance. The results revealed the existence of a clearance-dependent threshold rotational blade tip Reynolds, where the circumferential directionality of tip leakage flows reverses. The analysis of the convective heat flux field with varying operating parameters was achieved with Atomic Layer Thermopile sensors. The computed adiabatic parameters and unsteady contributors reveal high influence of the temperature field on the convective heat flux mechanisms. Lastly, the evaluation of the unsteady terms with tip clearance unveil the shift of thermal loads from the pressure to the suction side of the blade tip.</p><p dir="ltr">The achieved results have provided valuable insight into the underlying aerothermal mechanisms governing the tip clearance region, as well as connections with tip clearance size that could potentially be implemented on engine application systems.</p>