Determination of optimum specific thrust for civil aero gas turbine engines: a multidisciplinary design synthesis and optimisation

Abstract

A systematic methodology for the determination of optimum specific thrust of civil turbofan engines is presented. The optimum is defined as the specific thrust at which the engine direct operating cost is minimised. Based on publicly available data and clean‐sheet analysis, the developed method provides a rationale for the values of specific thrust found in existing engines and the basis for future designs. The optimum specific thrust determined here complements the thermodynamic optimisation strategy for engine parameters developed in a previous publication by Guha. The process of optimisation thus involves a complex multidisciplinary methodology involving aerodynamics, thermodynamics, structures, system integration, economics, legislations, and other design and operational issues. This study utilises two models: the fixed aircraft rubber engine model which simulates the retrofitting of new engines to a current airframe, and the rubber aircraft rubber engine model which simulates the thermodynamic optimisation of the engines alongside the optimisation of the airframe dimensions. Both models demonstrate that as the design range of the aircraft increases, the optimum value of specific thrust decreases. As fuel prices rise, the optimum value of specific thrust reduces further, taking it to levels where radical changes in engine design and integration would be necessary.