Hot streaks evolution in a high pressure axial turbine stage

Being most of the aero-engines featured by discrete position of fuel injectors, the flow at the combustor outlet has a non-uniform temperature distribution combined with a high turbulence level. Such turbine inlet distortion generates major aerothermal changes within the turbine vane and rotor, leading to possibly huge variations of secondary flows, blade loading, heat transfer, aerodynamics, and efficiency. The lack of confidence in foreseeing the hot streaks impact results in the application of extra safety margins, affecting negatively the turbine performances and efficiency. Although considerable efforts were made to study the hot spots effect downstream the statoric row, there is relatively little known for what concerns the flow field at the rotor outlet. Thanks to the High Speed Test rig at 𝐿𝐹𝑀 (Laboratory of Fluid Machines) of Politecnico di Milano, an aero-engine simulation can be performed without the presence of real combustors but, the hot streaks are generated through a device called 𝐸𝑊𝐺 (Entropy Wave Generator), injecting directly hot air at the turbine inlet. The purpose of our thesis is to fully characterise the flow field downstream the turbine first 𝐻𝑃 (High Pressure) stage rotor, from a thermodynamic and fluid dynamic point of view. Since previous thesis works performed measurements regarding similar topics, there was no need of building new probes, being the available ones already tailored for the High Speed Test Bench. Initially, the hot streaks were injected as continuous streams and their impact at the rotor outlet measured by temperature and pressure probes. Then, pulsating hot jets were introduced at turbine inlet, requiring prompter instruments. In this configuration, not only the flow field downstream the rotor was studied but, also the one upstream the turbine, in order to understand precisely the incoming disturb. The instrumentation used in this work were realised and calibrated inside the 𝐿𝐹𝑀; for the data acquisition and elaboration procedures both a 𝐹𝑜𝑟𝑡𝑟𝑎𝑛 and 𝐿𝑎𝑏𝑉𝐼𝐸𝑊 programs were implemented. Finally, it is worth noticing that measurements taken on this rig, and partially during the present test campaign, represent a unique data set available to the scientific community, especially the aero-acoustic one.