Nowadays total inlet temperature of gas turbine is far above the permissible metal temperature; as a consequence, advanced cooling techniques must be applied to protect from thermal stress and to reduce the risk of creep failure, oxidation and corrosion of components located in the high pressure stages, such as first vane. Film cooling has been widely used to control temperature of high temperature and high pressure vanes. In a film cooled vane the air taken from last compressor stages is ejected through discrete holes to provide a cold layer between hot mainstream and turbine components. A comprehensive understanding of phenomena concerning the complex interaction of hot gases with coolant flows in a vane passage plays a major role in the definition of a well performing film cooling scheme.

The aim of this study is the measurement of adiabatic effectiveness on the first stage vane of a heavy duty GT by means of coolant concentration technique based on Pressure Sensitive Paint (PSP). The investigation of coolant distribution on airfoils and platforms was done in order to make feasible possible optimizations and to validate numerical design tools. The experimental analysis was performed on a static test article replicating an annular sector made up of two cooled airfoils and three passages. An actual first stage vane (scale 1:1) with complete internal cooling scheme has been tested at different coolant conditions and imposing two values of density ratio (DR = 1.0;1.5). Film protection was generated by a showerhead on the leading edge and by cylindrical holes on pressure and suction side and on the platforms; finally a cutback with elongated pedestals was employed for the protection of the pressure side trailing edge. Results, reported in terms of detailed 2D maps of film cooling effectiveness and averaged trends, point out the effect of coolant-to-mainstream mass ratio and density ratio. Beyond the results obtained in this specific vane geometry, the use of PSP was proven to be a promising technique for direct measurements on real geometries: as a matter of fact, the opportunity to get detailed results of pressure and adiabatic effectiveness distributions is of outstanding importance for the design and optimization of vanes and blades cooling systems.

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