Design, Validation and Verification of Film Cooling on Gas Turbine Rotor Endwall

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