External and Internal Cooling Techniques in a Gas Turbine Blade - An Overview

Gas turbine engines are widely used in propulsion of aircraft and power generation. The thermal efficiency and power output of these engines predominantly depend upon the turbine inlet temperature (TIT). Increase or decrease in TIT affects the efficiency and power output to a great extent. Gas turbine engines currently operate at TIT ranging from 1200°C to 1500°C which is way above the melting point of blade material. Safe operation of these engines at elevated temperatures have been made possible by efficient cooling of blades, protection of blade surfaces by application of thermal barrier coatings (TBC) and advancement in blade metallurgy. Due to rapid economic and industrial growth, engines with the capability to operate at higher TIT would be required in future. Also, the metallurgy of the blade and thermal barrier coatings are required to be developed further to ensure reliable operation under harsh conditions. Different blade cooling techniques and the influence of various parameters on the effectiveness have been discussed in the literature. This paper aims to holistically address the various facets of turbine blade cooling and its operational parameters as available in the literature. Keywords—Airfoil; Thermal Efficiency; Power output; Nusselt number; Reynolds number