The transpiration cooling for blades of high temperatures gas turbine

Abstract

Gas turbines are rapidly becoming the choice for current and future power generation systems, because they offer efficient fuel conversion and reduced cost-of-electricity. Both of these advantageous features are related to the development of gas turbines with higher firing temperatures and pressure ratios [Keppel, VGB Kraftwerks-technik 74, 324 (1994); Batenin et al., Thermal Engng 40, 790 (1993); Styrikovich et al., Thermal Engng 42, 838 (1995)]. The key to the successful evolution of gas turbine systems is a strong technology base focused on two critical areas: the introduction of new materials and/or the usage of steam for significant increases of turbine blades cooling. Aircraft engines have continued to push both materials and air-cooling technology to achieve operating conditions significantly higher than those introduced into commercial industrial/utility gas turbines. An alternative approach for commercial gas turbines is to move to an alternate cooling medium, e.g. steam [Batenin et al., Thermal Engng 40, 790 (1993)]. The use of steam (would require a change in design concept) would introduce the potential for significant increases in firing temperature without the losses associated with increased cooling air extraction. Transpiration gas cooling was selected for the critical high-temperature turbine blade. Cooling gas effused through a porous wire mesh skin to create an insulating film or boundary layer on the outer airfoil surfaces. To optimize steam usage, penetration of porous skin was selected to provide only that quantity of steam to meet constant wall temperature at the local gas steam temperature and pressure conditions. The transpiration gas-cooled blade concept had demonstrated its ability to maintain safe metal temperatures when operating at very high gas stream temperatures. The goal of 60% thermal efficiency for a gas turbine power plant is a major challenge for engineers, but developments to achieve this are already under way.