The quest for higher performances and durability of modern aero-engines requires the understanding of the complex aero-thermal flow experienced in a multi-row environment. In particular, the high and low pressure turbine components have a great impact into the engine overall performance, and improvements in the turbine efficiencies can only be achieved through detailed research on the three-dimensional unsteady aerodynamics and heat transfer. The present thesis presents an experimental study of the aerothermodynamics in one and a half turbine stage, focusing on: the aero-thermal flow in the overtip region of a transonic highly loaded high pressure (HP) rotor, and the aerodynamics and heat transfer of an innovative low pressure (LP) stator with a multi-profile configuration placed downstream of the high pressure turbine, within an s-shaped duct.
Advanced instrumentation and measurement techniques were used and developed to perform the experimental investigation in a short-duration turbine test rig where both high spatial and time accuracy is indispensable. The flow field at the rotor shroud was investigated with simultaneous measurements of heat transfer, static pressure and blade tip clearance by using fast response pressure, wall temperature and capacitance probes. Through repeat experiments at the same turbine operating point, the time-averaged and time-resolved adiabatic wall temperature and convective heat transfer coefficient were evaluated.
In the frame of new engine architectures, a novel stator for a LP turbine is proposed with a multi-splitter layout that represents a new design solution towards compact, lighter and performing aero-engine turbomachinery. It contains small aero-vanes and large structural aerodynamic airfoils which are used to support the engine shaft and house service devices. The research focuses on the experimental investigation of the global performance, aerodynamics and thermodynamics of this novel HP-LP vane layout. The turbine was tested at three operating regimes depending on the pressure ratio and the rotational speed. Time-averaged and time-resolved surface pressure and heat flux measurements at the mid-section of the multi-splitter stator were used to characterize the steady and unsteady aero-thermal flow field. State-of-art CFD simulations were used to support the analysis and the understanding of the complex phenomena that characterize the flow physics and assess the efficiency of the structural LP vane at design and off-design conditions.
The goals of the research were to provide guidelines to design future aero-engines and promote the understanding of the flow physics in transonic turbine multi-row environments through analysis of the experimental data and comparison with the numerical models. The study provides an extensive experimental database to improve and validate turbomachinery CFD simulations.