Thermodynamic performance evaluation of gas turbine cycle with transpiration cooling of blades using air vis-à-vis steam

Abstract

Gas turbine blade cooling has major importance in improving the gas turbine cycle performance by an increase in turbine inlet temperature (TIT). Among different cooling techniques available, the convection and film cooling are the most widely used techniques. Studies have shown that transpiration cooling technique uses the coolant more effectively than the film and convection cooling techniques. The present study deals with the performance evaluation of gas turbine cycle with transpiration cooling of gas turbine blades. A comparison has been made using air and steam as cooling mediums. Cycle performance has been evaluated in terms of overall efficiency and specific power. Literature shows that in existing gas turbine blade cooling models the effect of radiation from higher temperature gases is usually neglected. However, the radiation occurs due to presence of high-temperature combustion products primarily comprising of CO2, NO x, and H2O. The present article evaluates the gas cycle performance taking radiation effect into account. A computer code ‘GTANALYS’ has been developed to perform all the computations. The results show that for the given conditions steam appears to be better coolant compared to air. For a TIT of 1700 K and cycle pressure ratio of 32, the steam-cooled cycle efficiency is about 2.58 per cent higher than air-cooled cycle efficiency.