The importance of cooling technology in propulsion and power systems

Turbine cooling is the breakthrough technology for gas turbine engines and although the turbine engine and cooling are considered mature technologies, to date they have only achieved about 60 to 70% of the cycle advantage available. Moreover, great improvements have been made in hot section materials and protective coatings, yet without hot section cooling, the high thrust to weight war fighter engine and the high by-pass ratio turbofan engine would be greatly compromised. Specifically, the level of combustor exit temperature of today's engines which is key for improved cycles would be limited to less than 2300 deg F using today's best materials and alloys. Air cooled turbine cooling technology utilizes convection in conjunction with film cooling to achieve combustor exit temperatures at least 1000 deg F higher than the highest combustor exit temperature that could be achieved with just materials alone. Moreover, a stoichiometric turbine would be yet another 1000 deg F higher. Thus, to continue the trend towards stoichiometric capability, hot section cooling technology will be a key ingredient. The open system air cooling technology is comprised of convection and film cooling. Although convection is near its maximum potential, film cooling still has about 50 to 60% of its potential remaining to be utilized. Thus, improved air-cooled technology will most likely concentrate on improved film cooling capability. In addition, closed loop cooling systems will also probably be revisited.