This paper describes the design process carried out to introduce film cooling coverage on the hub platform of a first turbine blade in order to protect from hot gas corrosion the trailing edge platform region. The different steps described consist in a design phase, a validation by experimental tests, the production follow up and verification feedbacks. The first stage endwall is a critical region due to secondary flows overheating; critical areas have been identified by 3D thermal analysis and confirmed through damage reports. A design phase has been carried out to determine the cooling holes configuration in terms of position, number, inclination and diameter. A CFD analysis allowed to define the hot gas streamlines near the pressure side fillet region in order to identify the best holes arrangement to ensure a proper thermal coverage; the thermal effectiveness and coverage length has been subsequently verified by means of an experimental activity developed by University of Bergamo. On the basis of the experimental results a 3D thermal analysis of the new holes configuration has highlighted the improvement in terms of local wall temperature reduction. Finally the new film holes have been introduced in the machining cycle of the blade and realized by electrochemical drilling. During a maintenance inspection after 20000 operating hours an endoscope investigation has confirmed the improvement obtained, showing no substantial signs of overheating.
In the present paper the influence of geometrical deviations, related to the manufacturing process or to a different hole positioning over the vane surface, and of coolant Reynolds number on flat plate film cooling through shaped holes are experimentally investigated. Hole geometrical parameters, such as the length of the cylindrical section, hole injection angle, lateral and forward expansion angles were varied and tested for blowing ratio M values between 1.0 and 2.0, also changing the coolant Reynolds number. The dual-luminophore Pressure Sensitive Paint (PSP) technique was used for measuring the adiabatic film cooling effectiveness distribution. Compared with the standard geometry, the V-shaped hole was shown to produce a better thermal protection, especially in the near hole region. Effectiveness is strongly affected by relatively small changes in the hole geometry, like the length of the cylindrical section and the forward expansion angle. A critical coolant Reynolds number was also identified, whose value changes depending on the hole geometry.
The present paper reports on an experimental investigation carried out at Bergamo University Energy system and turbomachinery laboratory aiming to assess the aerodynamic and heat transfer performance of a high pressure nozzle vane cascade without and with platform cooling. Information collected from solid vane testing was used to design a first platform cooling scheme made of cylindrical holes. The cooling scheme was first aerodynamically tested to quantify its impact on secondary flows and related losses for variable injection condition. Heat transfer performances were then assessed through the measurement of the adiabatic film cooling effectiveness and of the convective heat transfer coefficient. From these data, the Net Heat Flux Reduction (NHFR) parameter was computed to critically assess the cooling scheme. The collected data set is significant for the design process, as it is useful for CFD validation and for the setting up of correlations. In particular, a MFR = 0.7% resulted to be the best injection condition for this geometry, being a compromise between aerodynamic loss augmentation, a good thermal protection inside of the passage and a limited heat load increase to the end wall.
This paper describes an experimental activity carried out to investigate the potential of V-shaped holes for film cooling a high-pressure nozzle guide vane. The newly designed V-shaped scheme was compared with a standard laidback fan-shaped holes. The influence of showerhead cooling was also assessed. Different injection conditions were examined under the same cascade operating condition using CO2 as coolant. The quality of holes geometry and their discharging behavior was first characterized. Then dual luminophore Pressure Sensitive Paint (PSP) was used for measuring the adiabatic film cooling effectiveness all over the vane surface. Results of the current work showed that using a V-shaped hole configuration would give nearly the same surface protection as standard shaped holes with a reduced number of holes and, thus, at lower coolant flow consumption.
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