The Influence of Humidity on the Creep Life of a High Pressure Gas Turbine Blade: Part I—Heat Transfer Model

The cooling of high temperature gas turbines has been the subject of intensive work over the past few decades. Analysis of the metal temperature of cooled blades requires the solution of the equations governing the heat flow through the blade given the internal and external distributions of the boundary gas temperatures and heat transfer coefficients. An analytical model to investigate the influence of Water Air Ratio (WAR) on turbine blade heat transfer and cooling processes (and thus the blade creep life) of industrial gas turbines is presented. The method is based on a blade with convective cooling and a thermal barrier coating (TBC). The approach is based on engine performance, heat transfer models (hot side and cold side model), in addition to a method that accounts for the changes in thermal conductivity, viscosity, density and the gas properties of moist air as a function of WAR. The evaluation of heat transfer data in this model is considered by using non-dimensional parameters namely: Reynolds number, Nusselt number, Stanton number, Prandtl number and other related parameters. The aim of this paper is to present an analytical model to investigate the influence of humidity on the turbine blade heat transfer and cooling processes which, in turn, affect blade creep life. The developed model can be used to assess the main parameters that influence blade cooling performance, such as cooling methods, alternative cooling fluids, blade geometry, gas properties and material and thermal barrier coatings. For a given off-design point, the WAR was varied from dry to humid air (air/water vapour mixtures). The whole cooled blade row is regarded as a heat exchanger with the presence of TBC subjected to a mainstream hot gas flow from the combustion chamber.