The modern trends of gas turbine engines focus on increased turbine inlet temperatures in order to reduce the specific fuel consumption and increase the overall performance of the engine. However, operation at very high temperatures reduces the life time of turbine vanes and blades while the allowable temperature level of the cycle is limited by the melting point of the materials. Therefore, turbine blade cooling is necessary to reduce the blade metal temperature to acceptable levels for the materials increasing the thermal capability of the engine. Due to the contribution and the development of turbine cooling systems, the turbine entry temperature (TET) has been over doubled over the last 60 years.
Turbine blade cooling can be classified in two major sections: The internal, where the heat is removed by a variation of convection and impingement cooling configurations, where high velocity air flows and hits the inner surfaces of the turbine vanes and blades, and the external blade cooling, where cold air is injected through the film cooling holes on the external blade surface in order to create a thin film cooling layer. A wide range of internal and external cooling arrangements has been applied in the past; however, the aim in both cases is to keep the entire blade cool enough and also to ensure that temperature gradients within the blade (which might lead to thermal stresses) are kept to an acceptable level.