MODELING OF BLADE COOLING ON THE FIRST TWO TURBINE STAGES AND THE COOLING EFFECT ON THE GAS TURBINE PERFORMANCE
In power generation with gas turbines, the firing temperature or turbine inlet temperature has been increased significantly in recent decades for high efficiency as well as power production. To maintain the metal temperature under a certain limit, blade cooling needs to be implemented, which, however, can reduce the amount of fuel input and lead to aerodynamic losses due to flow mixing. Therefore, it is critical to find the right cooling air flow rate for each row of blades. In this study, the cooling air flow is modeled by fixing the allowable metal temperature for a gas turbine with cooling applied to its first two stages. Film cooling is used for the first stage, including both stator and rotor blades. To be consistent with the physical phenomena, the film cooling effectiveness is considered a function of the cooling flow rate, which is different from some other studies. For the second stage, the internal convection cooling is applied. The cooling air after a given row is assumed to mix with the main stream, which lowers the average flow temperature. After a desired turbine inlet temperature is selected, the cooling air needed is calculated for each row of blades. The performance of the gas turbines is then analyzed with a focus on the thermal efficiency and power output. It is found that majority of cooling air (more than 50%) is used for cooling of the first-stage vane blades. The efficiency of blade cooled gas turbines with a regenerator increases 8% at a pressure ratio of 10.