Proceedings of Montreal 2018 Global Power and Propulsion Forum 7 th – 9 th May, 2018 www.pps.global GPPS-NA-2018-0039 A PRELIMINARY STUDY INTO TURBOFAN PERFORMANCE WITH LP-HP POWER EXCHANGE Hossein Balaghi Enalou University of Nottingham Hossein.Balaghienalou@nottingham.ac.uk Nottingham, UK Serhiy Bozhko University of Nottingham Serhiy.Bozhko@nottingham.ac.uk Nottingham, UK Mohamed Rashed University of Nottingham Mohamed.Rashed@nottingham.ac.uk Nottingham, UK Ponggorn Kulsangcharoen University of Nottingham Ponggorn.Kulsangchareon@nottingham.ac.uk Nottingham, UK ABSTRACT Once an engine is designed, its Low Pressure (LP) and High Pressure (HP) shaft speeds are inevitably thermodynamically coupled which imposes certain operational constraints. These spools are not mechanically connected, however, in future more electric aircraft with electrical machines linked to both HP and LP shafts it is possible to transfer power between them electrically seeking for optimized operation depending on Engine Operating Mode (EOM). This paper investigates possible achievements of the novel configuration of power circulation between shafts using turbofan model, developed by Inter-Component Volume (ICV) method. Results show that a considerable improvement can be achieved not only in fuel consumption but also in surge margin of compressors along with providing ability to have compatible thrust with flight mission. INTRODUCTION In order to accomplish ambitious overall aircraft fuel burn goals, hence environmental impact, propulsion technology plays prominent role which emphasizes the importance of its further improvements. Turbofans, as primary source of propulsion, are designed for cruise phase, which consumes most of an aircraft’s fuel. However, after assembly of all components, where sealing and rotor dynamic issues depend on high manufacturing and assembly tolerances (Lattime and Steinetz, 2002), there is a possibility that an engine will deviate from its design point for some of its components. With all the improvement in CFD (Computational Fluid Dynamics) analysis, the deviation is not expected to be significant, however, there is still room for improvement. Another important fact is that with aging of an engine, its optimum point of operation shifts to a different point with different shaft speeds which can either decrease efficiency or safe margins. Normally, HP shaft components are more susceptible to wear out due to higher speed and pressure operation condition (Kurz and Brun, 2001; Meher-Homji et al., 2001). On the other hand, having been designed for Aerodynamic Design Point (ADP), an engine operates in sub- optimal condition during low power settings at other flight phases, such as taxiing and descent, creating inconsistent thrust with aircraft mission on top of being fuel inefficient. Engine shaft speeds are designed to be matched at ADP to keep the air mass flow balanced between Low Pressure Compressor (LPC) and High Pressure Compressor (HPC) (Razak, 2007; Walsh and Fletcher, 2008). LP and HP shafts are not connected mechanically, while their speed are coupled aero-thermodynamically within the engine which enforces unmatched shaft speeds at low speed settings. This as a consequence creates imbalanced air mass flow between LPC and HPC. In order to overcome this problem designers are obliged to implement bleeding between LPC and HPC which consequently limits the engine at a permissible minimum speed. If the engine speed falls below the minimum level, due to increase in required bleeding, core airflow across High Pressure Turbine (HPT) and Low Pressure Turbine (LPT) will not be adequate to produce power to drive compressors which results in an engine not being self-sustained anymore. Therefore, for engine operation at low speed settings, undesirable measures are taken due the imminent thermodynamic coupling between shaft speeds for which an engine pays off both in terms of fuel efficiency and excessive thrust at low speed settings. However, single dc bus Electric Power System (EPS) architecture with electrical machines on both LP and HP shafts (Gao and Bozhko, 2016a; Gao et al., 2015; Gao et al., 2016b) provides the ability to transfer power between shafts electrically to decouple shaft speeds. This novel configuration is expected to:  enable engine core components to operate closer to their optimum design point after aging  reduce the fuel burn during low speed settings