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

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VKI PHDT 2014-09, Fabrizio Fontaneto, Aero-thermal performance of a film-cooled high pressure turbine blade/vane: a test case for numerical codes validation, ISBN 978-2-87516-083-6, 167 pgs

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

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

PhD Thesis from the von Karman Institute / University of Bergamo, May 2014, ISBN 978-2-87516-083-6, 167 pgs


Abstract

Nowadays companies are making a massive use of Computational Fluid Dy- namics (CFD) since the early stages of the development of new components. Given therefore the critical role that numerical codes are playing, their re- liability must be rigorously checked through detailed comparisons between numerical and experimental results. The present thesis concentrates on the experimental activity carried in the frame of two different measurement campaigns, both focused on the creation of an experimental test-case for turbomachinery codes validation.

The first experimental activity, funded by “Ansaldo Energia” and carried out at the Energy Systems and Turbomachinery Laboratory of the University of Bergamo (Italy), dealt with the characterization of the effect that the end- wall cooling system of a high pressure turbine rotor has on both, the thermal and the aerodynamic performance, with a particular attention paid to the study of the interaction between the cooling jets and secondary flows. Starting from the original geometry, a full-scale model was designed and tested in an open-loop suction-type wind tunnel as a seven blade linear cascade. Aerodynamic measurements, performed by means of a 5-hole miniaturized pressure probe, evidenced a marked asymmetry of the secondary flows be- tween the upper and the lower semi-channels. The latter had to be related to the presence of the fillet between the blade and the cooled endwall and it demonstrated to provide a significant reduction of the aerodynamic losses. 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 con- fined in the boundary layer. Such a result was confirmed by the adiabatic effectiveness distribution which was retrieved by thermochromic liquid crystals. The thermal protection was continuously growing with the injection rate and no separation was identified. The high performance of the cooling system had to be related to the extreme tangential arrangement of the holes. In the end, a good agreement was found between the experimental data and the results of simulations run by the company.

The second measurement campaign was held at the von Karman Institute for Fluid Dynamics (VKI) (Belgium) and funded by the Japanese Central Research Institute of Electric Power Industry (CRIEPI). A film-cooled transonic turbine vane was investigated in a five blades linear cascade configuration and at engine-like conditions in terms of Reynolds number and Mach number. The inlet free-stream turbulence was fully characterized by means of hot-wire anemometry: the evolution along the inlet channel of the turbulence intensity, of the turbulent kinetic energy and of the turbulence scales all showed results in complete agreement with partial past results and literature. 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, with a weak increase in terms of aerodynamic losses. In particular, it has been demonstrated how, in supersonic conditions, the presence of a strong shock in the rear part of the suction side is responsible for a marked degradation of the performance of the cascade. Thin-films thermometers have been used to retrieve the blade convective heat transfer coefficient (h) distribution. The non-cooled tests demonstrated that, for every main-stream condition, the tripping effect of the film-cooling holes is the responsible for a transition of the boundary layer state. The thermal protection of the suction side always increases with the injection rate, showing therefore a high resistance to separation. On the pressure side, on the contrary, the portion of the blade surface placed immediately downstream the injection point is characterized by values of h higher than those of the non-cooled case: already at low injection rates, the coolant momentum is high enough to break down the boundary layer, putting therefore in direct contact the blade surface with the hot main-stream. In any case, the rear part of the pressure side always benefits from an enhanced injection.

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