Approximately Calculating Optimum Pressure Ratios for Various Gas Turbine Cycles

Abstract

In designing the gas turbine engine, it is important to know the rough relationship between the specific output, thermal efficiency, and pressure ratios before setting about calculating the practical cycle. In general, the specific output and the thermal efficiency have their maximum values at certain pressure ratios. The pressure ratios for these maximum values, however, differ in the case of the specific output from the thermal efficiency even in the same type of gas turbine. This paper presents the equations for the optimum pressure ratios of the specific output and thermal efficiency which are obtained for seven types of single-shaft gas turbines. Furthermore, a change in the forms of the curves is made clear by the numerical calculations for the specific output and thermal efficiency near the range of optimum pressure ratios. From the results of this paper, the optimum pressure ratios for every type of single-shaft gas turbine can be easily determined from the thermodynamical point of view.