Analysis of Temperature in a Turbine Rotor Blade and Effects of Cooling Hole Blockage on Surface Degradation and Life

The improvement of efficiency has always been the aim of jet engine design, as it enhances performance and reduces fuel consumption and, therefore, environmental impact and costs. The turbine entry temperature is one of the most influential factors on the performance and has significantly increased over the years. The trend to push it towards new extremes represents a huge challenge for turbine blades, especially those of the first stage high-pressure turbine, which must be provided with a complex cooling system in order to withstand the high thermal loads. Potential malfunctions of the cooling system, such as the blockage of the cooling holes, have to be included in the design since they can lead to an overheating of the blade and a potential failure of the entire turbine. The present thesis aims at accurately calculating the temperature distribution in a rotor blade of a Rolls-Royce jet engine in the middle thrust class and assessing the effects of the film cooling hole blockage on it. The objective is to accurately predict the damage rate and the consequent limitation on the blade life, in terms of flight cycles allowed, in order to ensure safe operations. For this purpose, the cooling technologies and the failure mechanisms of the blade are first investigated. A 3D conjugate heat transfer model of the component is created using the commercial software STAR-CCM+ provided by Siemens™ in order to predict the heat transferred between the solid surface, the internal coolant and the external gas. This allows to compute the blade temperature and, therefore, detect the highest temperature areas. Finally, a sensitivity study is carried out to evaluate how different levels of hole blockage influence the deterioration of the tip, one of the most overheated parts of the blade. The results show that the tip damage increases due to holes blockage, not following a linear trend, but with a rapid growth over 30% blockage. The resulting limitation of the blade life is forecasted and reported as a function of the level of blockage, with the aim of being added to the life cycle model of the engine. This predictive approach will enable an optimised maintenance, reducing engine down-time and ultimately life-cost.