Film Cooling and Cold Streaks Tracking on a Fully Cooled Nozzle Guide Vane Under Representative Combustor Outflow Conditions

Abstract

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.

Unsteady Flows and Component Interaction in Turbomachinery

“…Several activities were performed in a test rig designed by Cubeda et al [79] (see Section 3.2.1) to analyze the redistribution of the hot flow in the cooled vane passage in the presence of a strong residual swirl. Babazzi et al [80] used Pressure-Sensitive Paint (PSP) to evaluate film cooling performance and an oxygen concentration probe to track cold streak migration, and demonstrated that in the investigated configuration, low-coverage areas appeared on the suction side due to swirl-induced alterations of the streamlines. The presence of a strong residual swirl modified the stagnation line shape and position, thus altering vane load distribution [80] and the heat transfer coefficient maps [81].…”

“…Babazzi et al [80] used Pressure-Sensitive Paint (PSP) to evaluate film cooling performance and an oxygen concentration probe to track cold streak migration, and demonstrated that in the investigated configuration, low-coverage areas appeared on the suction side due to swirl-induced alterations of the streamlines. The presence of a strong residual swirl modified the stagnation line shape and position, thus altering vane load distribution [80] and the heat transfer coefficient maps [81]. Moreover, the unsteady nature of the swirling flow generated a fluctuating map of adiabatic effectiveness that was not represented by the time-averaged one.…”