Assessment of Modulated Pre-swirl System in the Turbofan Engine by a Multi-dimensional Coupled Model

The design of contemporary aero-engine is facing challenges regarding larger flight envelope and less fuel consumption. Considering that the components in mainstream are approaching their performance limits, the secondary air system (SAS) modulation has become an attractive option for efficiency enhancement at off-design conditions. The pre-swirl system is of great importance for cooling air supply to the turbine disk and blades, which extracts a considerable amount of high-quality cooling air from the compressor and rarely contributes to the thrust. This study aims to investigate the influence of modulated pre-swirl system on the fuel consumption and turbine disk life. A multi-dimensional coupled model of the turbofan engine has been developed, which contains an engine performance code, a SAS network and a high-fidelity turbine disk. A commercial finite element solver was adopted to capture the temperature and structure fields. CFM56, a typical civil turbofan engine, was selected as the reference object, and flight missions with different modulated configurations are simulated. The results reveal that reducing the cooling air flowrate of pre-swirl system effectively decrease the combustor outlet temperature and the fuel consumption, however these benefits are probably at the expense of the turbine disk life. Under the equivalent thrust at cruise condition, a 20% reduction of the pre-swirl nozzle cross-sectional area decrease the cooling air flowrate by 18%, resulting in specific fuel consumption dropping by 0.39%, and the penalty probably is the loss of disk creep life, meanwhile, the disk fatigue life seems to be insensitive to the cruise modulations. Additionally, the relative profit RP is proposed to provide a new view of optimizing the cooling air modulation.