Aerodynamics and Heat Transfer Inside a Gas Turbine Mid-Passage Gap

Abstract

Gas turbine blades and vanes are typically manufactured with small clearances between adjacent vane and blade platforms, termed the mid-passage gap. The mid-passage gap reduces turbine efficiency and causes significant additional heat load into the vane platform. This paper presents a new low-order analytical model to quantify the effects of the mid-passage gap on aerodynamics and heat transfer, based only on geometric features and the passage static pressure field. This model is used to calculate losses and heat transfer due to the gap and to derive ideal distributions of purge flow which prevent ingress into the gap. A further simplified estimation method for the effect of gap flow is also presented, so that for any machine the significance of the gap can be quickly assessed based only on geometry and operating conditions. The analysis is validated against both an experimental campaign in a high-speed linear cascade and Reynolds-averaged Navier–Stokes computational fluid dynamics.