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FILM COOLING AND COLD STREAKS TRACKING ON A FULLY COOLED NOZZLE GUIDE VANE UNDER REPRESENTATIVE COMBUSTOR OUTFLOW CONDITIONS


 The pronounced non uniform temperature distribution in the core engine flow path is a recurring problem of gas turbine engine design process, as it directly affects turbine performance and lifetime. Specifically, turbine entry conditions are usually characterised by severe temperature distortions, often referred to as hot and cold streaks. Temperature distortions remain an issue even at the exit section of the NGV, with additional cold streaks coming from the vane cooling system. Various studies focus on the description of streaks migration through a direct investigation of the thermal field, providing a global evaluation of the phenomenon. As a deeper understanding is often required, experimental techniques based on the detection of tracer gases can be successfully adopted. In this study, a realistic combustor outlet swirl profile was imposed on a fully cooled NGV cascade to analyse both film-cooling behaviour and cold streaks migration. A concentration probe based on the fluorescence behaviour of an oxygen sensor was here employed to track the position of the film cooling flows at the NGV cascade exit plane, while the adiabatic film-cooling effectiveness was evaluated on the NGV surfaces employing the PSP technique. Overall, the swirling structure strongly affect both the film-cooling behaviour and cold streaks migration through and downstream the vane. The importance of examining the unsteady aspect is also highlighted. A global understanding of the occurring phenomena is therefore provided, as well as significant pieces of information useful for the design phases of both the NGV and the following rotor cascade.