The Effect of Turbine Blade Cooling on the Performance of Recuperative Cycles for Gas Turbines Applications

Abstract

Nowadays the constantly increasing demand for energy production has a strong impact on the environmental pollution. Therefore, the development of more efficient gas turbines is a key factor for decreasing pollutant emissions. The increased combustion temperature can significantly improve gas turbine cycle efficiency. However, this temperature is limited by the maximum allowable temperature of the turbines blades material. Another way to improve cycle performance is the use of gas turbine recuperation by the installation of heat exchangers for preheating the cold air before it enters the combustor which can lead to improved efficiency, important fuel reduction and thus, to low emissions. In this work the impact of the turbine air cooling requirements on different recuperative cycles efficiencies is investigated. A thermodynamic cycle analysis tool capable to calculate the performance of gas turbines cycles with and without the inclusion of the effects of cooling air flow rates is developed. In the analysis three recuperative cycles are investigated. The first configuration under investigation is the conventional recuperative cycle in which a heat exchanger is employed downstream the last turbine, in the second configuration, the alternative recuperative cycle, the heat exchanger is placed between the low pressure and the intermediate pressure turbine while in the last configuration, the staged heat recovery recuperative cycle, two heat exchangers are installed, the first between the low pressure and the intermediate pressure turbine and the second downstream the last turbine. For the completeness of the work, the first part shows the cycles efficiency without including the coolant mass flow for the turbine. The second part focuses on the performance assessment of the recuperative cycles, by taking into consideration the demands for turbine blade cooling. A tool for the calculation of the required coolant flow rates for each turbine, based on the theory of Young and Wilcock, is presented. A detailed parametric study is conducted for a wide range of operational conditions by taking into account three different values of maximum allowable blade metal temperatures and the results of the thermodynamic cycles efficiencies with and without turbine blade cooling are compared and discussed. In the last part of the work a detailed model of a helicopter engine is presented and the impact of the coolant mass flow rates on the engine performance is examined.