Aero-thermal performance of a film-cooled high pressure turbine blade/vane: a test case for numerical codes validation

The present thesis concentrates on the experimental activity carried in the frame of two different measurement campaigns aiming to create an experimental test-case for turbomachinery codes validation. The first experimental activity was carried out at the University of Bergamo and dealt with the characterization of the aero-thermal performance of a film-cooled high pressure turbine rotor blade. Aerodynamic measurements, performed by means of a 5-hole miniaturized pressure probe, evidenced a marked asymmetry of the secondary flows between the upper and the lower semi-channels. Injection seemed not to affect at all the secondary flows pattern: at every injection rate, the cooling jets kept attached to the endwall surface and confined in the boundary layer. Such a result was confirmed by the adiabatic effectiveness distribution which was retrieved by thermochromic liquid crystals. The high performance of the cooling system had to be related to the extreme tangential arrangement of the holes. The second measurement campaign was held at the von Karman Institute for Fluid Dynamics (VKI) (Belgium). A film-cooled transonic turbine vane was investigated in a five blades linear cascade configuration and at engine-like conditions. The inlet free-stream turbulence was fully characterized by means of hot-wire anemometry. The aerodynamic performance of the cascade was assessed by traversing a 3-hole pressure probe in the downstream section. Injection was found to slightly enhance total pressure wakes. Thin-film thermometers have been used to retrieve the blade convective heat transfer coefficient (h) distribution. The non-cooled tests demonstrated that the tripping effect of the film-cooling holes is the responsible for a transition of the boundary layer. The thermal protection of the suction side always increases with the injection rate while the pressure side is showing values of h higher than those of the non-cooled case: at low injection rates, the breaks down the boundary layer.