Design Optimization of Blade Tip in Subsonic and Transonic Turbine Stages - Part I: Stage Design and Preliminary Tip Optimization

Abstract

Abstract Rotor blade tip has significant influence on turbine stage aero-dynamics and heat transfer. Most previous efforts have been based on low-speed cascade settings. However, more recent research on transonic blade tips exhibits distinctive flow features with qualitatively different performance sensitivities. These prompt two key issues of interest on the related flow conditioning. First, the contrast between a low-speed flow and a transonic regime highlights the relatively less studied high-subsonic regime, closely relevant to many realistic turbine designs. Second, the relative casing movement and upstream inflow conditions, known to have non negligible effects, indicate the need to examine a rotor blade tip in a realistic stator-rotor stage environment, which is also lacking. To elaborate the Mach number effect in the flow regimes of practical interest, we aim to examine a high subsonic stage in a direct and consistent comparison with a transonic one. To this end, a high subsonic stage (exit Mach number of 0.7) and a transonic (exit Mach number of 1.1) are designed at the same Reynolds number with a 3D parameterization and meshing system. The tip squealer height is used as a representative parameter to investigate the sensitivity of the stage aerothermal performance. The multi-objective optimization using the Kriging surrogated model is employed to identify the Pareto fronts for the stage efficiency and the heat transfer.